the distribution and speciation of iron along 6 e in the southern ocean abstract the distribution and speciation of iron was determined along a transect in the eastern atlantic sector 6 e of the southern ocean during a collaborative scandinavian south african antarctic cruise conducted in late austral summer december 1997 january 1998 elevated concentrations of dissolved iron 0 4 nm were found at 60 s in the vicinity of the spring ice edge sie in tandem with a phytoplankton bloom chiefly dominated by phaeocystis sp this bloom had developed rapidly after the loss of the seasonal sea ice cover the iron that fuelled this bloom was mostly likely derived from sea ice melt in the winter ice edge wie around 55 s dissolved iron concentrations were low 0 2 nm and corresponded to lower biological productivity biomass in the antarctic polar front at approximately 50 s a vertical profile of dissolved iron showed low concentrations 0 2 nm however a surface survey showed higher concentrations 1 3 nm and considerable patchiness in this dynamic frontal region the chemical speciation of iron was dominated by organic complexation throughout the study region organic iron complexing ligands l ranged from 0 9 to 3 0 nm fe equivalents with complex stability log k fe l 21 4 23 5 estimated concentrations of inorganic iron fe ranged from 0 03 to 0 79 pm with the highest values found in the phaeocystis bloom in the sie a vertical profile of iron complexing ligands in the wie showed a maximum consistent with a biological source for ligand production and near surface minimum possibly consistent with loss via photodecomposition this work further confirms the role iron that has in the southern ocean in limiting primary productivity

middle to late devensian glaciation of north east scotland implications for the north eastern quadrant of the last british irish ice sheet we present a review of over 175 years of research into the middle to late devensian weichselian glaciation of north east scotland based crucially on both its lithostratigraphic and geomorphic records the location of the region and surrounding seabed makes this unusually detailed record significant for deciphering the former interactions and dynamics of scottish and scandinavian ice within the north sea basin nsb which continue to be controversial a twelve stage event stratigraphy is proposed based on a parsimonious interpretation of stratigraphic relationships till lithology and regional clast fabrics striae subglacial bedforms ice marginal features and published geochronometry at critical sites the record of regional glaciation supports converging evidence that the north eastern quadrant of the last british and irish ice sheet biis reached its maximum spatial extent in the late middle to early late devensian and later re expanded following widespread internal glacial reorganisations marine transgression and partial retreat from the central nsb retreat was interrupted by several glacial readvances of limited extent field captured data helps identify important events that are not clearly resolved from remote sensing alone particularly regarding growth phases of the last glaciation

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

coastal lake records add constraints to the age and magnitude of the younger dryas ice front oscillation along the skagerrak coastline in southern norway

sequence stratigraphy in a marine moraine at the head of hardangerfjorden western norway evidence for a high frequency relative sea level cycle abstract the depositional architecture and stratigraphy of the haereid moraine a sedimentary ridge ca 1 5 km long and up to 113 m in height at the head of hardangerfjorden west norway have been reconstructed in a high resolution sequence stratigraphic framework information from ground penetrating radar gpr profiles outcrop sections and borehole data have been used in the analysis the basal forced regressive deposits comprise relicts of a gilbert type delta that commenced its development at the front of a grounded glacier on the seaward distal side of the ridge there is a major channel fill mouth bar complex covering large parts of the delta s former frontal slope and prodelta zone the complex occurs in the seaward lengthening of a fluvially incised channel and is interpreted as a lowstand to early transgressive succession of fluvial and fluvial estuarine facies the channel fill mouth bar complex and the dissected delta top have been planed off through transgressive ravinement and the delta top is overlain by an upvalley thinning sedimentary wedge 3 8 m thick and with a general landward onlapping and propagating internal bedform geometry this wedge is thought to be composed mainly of transgressive marine estuary mouth barrier facies on the landward proximal side of the ridge the transgressive deposits include a retrograding landward dipping foreset interpreted as relicts of a flood tidal delta overlain by possible washover fan deposits these deposits are again conformably overlain by laminated clay interpreted as the remains of a highstand mud drape the depositional sequence delineated in this study up to 20 m thick and comprising deposits of a lowstand wedge a transgressive and a highstand systems tract developed in response to a relative sea level rsl rise of 12 15 m this rsl rise which interrupted the general rsl fall following the deglaciation is correlated with the younger dryas transgression a regionally recorded sea level event the highstand mud drape was deposited as the rising rsl ultimately led to drowning of the moraine the highstand and transgressive deposits are erosively truncated by a thin gravelly lag deposited during final emergence in the early holocene

dissolved iron in the southern ocean atlantic sector abstract we report a comprehensive dataset of dissolved iron fe comprising 482 values at 22 complete vertical profiles along a 1 latitudinal section at the zero meridian in addition a shorter high resolution 00 09 surface section of the southernmost part of the transect 66 00 69 35 s is presented within the upper surface mixed layer the concentrations of dissolved fe vary between 0 1 and 0 3 nm an inverse trend versus fluorescence suggests significant fe removal by plankton blooms vertical mixing and upwelling are the most important supply mechanisms of iron from deep waters to the upper surface mixed layer at lower latitude 42 s there is a distinct maximum of 0 6 0 7 nm in the 2000 3000 m depth range due to inflow of north atlantic deep water in one region 55 s elevated dissolved fe found in the surface mixed layer is ascribed to the recent deposition of aeolian dust originating from south america close to the antarctic continent there is an indication of fe supply in surface waters from icebergs in the deep waters there is a strong indication of a hydrothermal plume of dissolved fe and mn over the ridge in the bouvet region 52 56 s in the weddell gyre basin the dissolved fe in the deep water is 0 47 0 16 nm in the eastward flow at 56 62 s and is lower with a value of 0 34 0 14 nm in the westward flow at high 62 69 s latitude at the edge of the continental ice sheet on the prime meridian the continental margin of the antarctic continent appears to be lesser source of dissolved fe than in any other place in the world this is likely because it is unique in being overlain by the extending continental ice sheet that largely prevents biogeochemical cycling

variations in the zn si record over the last interglacial glacial transition we examined the zinc content of diatom frustules as an indicator of past changes in surface seawater zn2 concentration zn si data of samples from three cores located in the south atlantic sector of the southern ocean spanning the last interglacial glacial transition are presented changes in the zn si record are linked to changes in the surface water zn2 concentration the source of variation in zn2 concentration appears to be via changes in deep water upwelling and circulation we rule out changes in phytoplankton productivity and aeolian dust input as a source of variation in the zn si record likewise the zn si data are not linked to shifts in the diatom species composition of the sediment or sediment preservation effects the zn si results presented do not support the zinc hypothesis there is no link between the uptake of co2 by phytoplankton as inferred from the 13c record and the zn si record

response of jakobshavn isbrae greenland to holocene climate change rapid fluctuations in the velocity of greenland ice sheet gis outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future this significant short term variability highlights the need for geologic records of preinstrumental gis margin fluctuations in order to better predict future gis response to climate change using 10 be surface exposure ages and radiocarbon dated lake sediments we constructed a detailed chronology of ice margin fluctuations over the past 10 k y for jakobshavn isbrae greenland9s largest outlet glacier in addition we present new estimates of corresponding local temperature changes using a continuous record of insect chironomidae remains preserved in lake sediments we find that following an early holocene advance just prior to 8 ka jakobshavn isbrae retreated rapidly at a rate of 100 m yr 1 likely in response to increasing regional and local temperatures ice remained behind its present margin for 7 k y during a warm period in the middle holocene with sustained temperatures 2 c warmer than today then the land based margin advanced at least 2 4 km between a d 1500 1640 and a d 1850 the ice margin near jakobshavn thus underwent large and rapid adjustments in response to relatively modest centennial scale holocene temperature changes which may foreshadow gis response to future warming

multi decadal retreat of greenland s marine terminating glaciers many marine terminating glaciers draining the greenland ice sheet have retreated over the past decade yet the extent and magnitude of retreat relative to past variability is unknown we measure changes in front positions of 210 marine terminating glaciers using landsat imagery spanning nearly four decades and compare decadal scale rates of change with earlier observations we find that 90 of the observed glaciers retreated between 2000 and 2010 approaching 100 in the northwest with rapid retreat observed in all sectors of the ice sheet the current retreat is accelerating and likely began between 1992 and 2000 coincident with the onset of warming following glacier stability and minor advance during a mid century cooling period while it is clear an extensive retreat occurred in the early 20th century a period of increasing air temperatures a comparison of our results with historical observations provides evidence that the current retreat is more widespread the onset of rapid retreat with warming relative to the slow and lagged advance with cooling suggests an asymmetry in the response of marine fronts to external forcing

macronutrient and trace metal geochemistry of an in situ iron induced southern ocean bloom abstract we have investigated the effect of iron supply and increased phytoplankton growth on the cycling of the macronutrients phosphate nitrate and silicic acid as well as the micronutrients copper cu nickel ni zinc zn and cadmium cd nutrient levels were measured in situ in an iron induced phytoplankton bloom at 61 s 140 e in the southern ocean iron release experiment soiree nutrient ratios upon arrival at the study site indicate that much of the seasonal phytoplankton productivity was by iron limited diatoms growing at low mean light levels the addition of iron fe induced a bloom that led to a draw down in the macronutrients in ratios consistent with the growth of diatoms under iron replete conditions none of the bioutilised trace metals cu ni zn or cd showed any indication of co limitation with fe of phytoplankton growth zn concentrations did not decrease by algal uptake as expected cd was partitioned to the particulate phase indicating consumption by the algae cd was preferentially utilised with respect to p with a cd p 5 8 interpretation of the cd ca data from the sedimentary record using this higher induced cd p value would imply even higher southern ocean surface water p during the last glacial maximum

late glacial and holocene 10be production rates for western norway we present a new regional calibration of the 10be production rate from two well dated surfaces insouthern norway a rock avalanche with 14c dated wood and a precisely dated younger dryas moraine c

seismic slip segmentation and the loma prieta earthquake we have plotted the cumulative seismic slip projected onto a vertical plane for earthquakes occurring during the last 20 years along 210 km of the san andreas fault that includes the section that moved in the loma prieta earthquake these plots illustrate the differences in depth and character of the seismicity between the locked and creeping portions of the fault or fault zone and define the segment upon which the loma prieta earthquake occurred working by analogy from the relation between pre main shock microseismicity and presumed main shock slip regions at parkfield and loma prieta we identify a segment on the san francisco peninsula where we believe the m 7 1838 earthquake occurred and which we believe may have accumulated sufficient strain that rupture should be expected in the coming decades

a role for scavenging in the marine biogeochemical cycling of zinc and zinc isotopes zinc zn and cadmium cd are important biologically active trace metals in the ocean to date the marine distributions of these elements have been understood primarily in terms of biological assimilation by growing phytoplankton and regeneration of sinking biological material initial studies of zn and cd concentrations and stable isotope ratios 66zn and 114cd have therefore focused on their use as simple tracers of assimilation and regeneration in the oceans however these two processes are insufficient to explain new data on the marine distribution of zn and 66zn here using the first high resolution paired marine depth profiles of zn cd 66zn and 114cd we suggest that scavenging of zn onto organic matter plays a major yet largely unconsidered role in the marine cycling of zn this hypothesis is supported by culture experiments which show that zn released from degrading phytoplankton is rapidly scavenged back onto organic matter and that adsorbed zn is isotopically heavier than the dissolved phase by 0 58 in contrast very little cd or phosphate was scavenged and cd isotopes were not significantly fractionated during degradation our hypothesis is further supported by one dimensional modeling which reproduces observed marine 66zn profiles with 1 of zn adsorbed to particles understanding how zn cycling in the oceans is a balance between assimilation scavenging and regeneration is necessary in order to investigate 66zn as a tracer of marine productivity we anticipate that paired analyses of 66zn and 114cd will prove to be valuable new tools in constraining patterns of global primary productivity providing key information for the marine carbon cycle during periods of past and present global climate change

rapid response of helheim glacier southeast greenland to early holocene climate warming recent changes in speed thinning and retreat rates of marine terminating outlet glaciers have raised concerns about the future stability of the greenland ice sheet establishing a longer term record of outlet glacier retreat rates is essential to provide a context for present day observations and to improve and constrain numerical models of outlet glacier behavior new exposure dating 10be of streamlined bedrock surfaces and glacial erratic boulders of sermilik fjord southeast greenland the present day drainage route of helheim glacier documents rapid retreat 80 m a 1 of this major marine terminating outlet glacier at the close of the last glaciation the glacier front retreated 80 km to within 20 km of the present day 2010 position of helheim glacier in 1 ka ca 10 8 0 3 ka ago retreat followed rapidly rising air temperatures at the start of the holocene and at this temporal resolution there is no evidence that fjord geometry influenced glacier behavior the significant response to climatic amelioration at the end of the last glacial suggests a high sensitivity to abrupt temperature increases which has major implications for the future stability of present day greenlandic outlet glaciers in a warming climate

unstable ice stream in greenland during the younger dryas cold event past present and future ice sheet stability is closely linked to the dynamic behavior of major draining ice streams and surrounding ice shelves while short observational records document the recent variability and acceleration of ice streams the long term dynamics of ice streams remain poorly documented here we date the pjetursson s moraine on disko island greenland to 12 2 0 6 ka and demonstrate that the jakobshavn isbrae ji ice stream collapsed during the middle of the younger dryas yd cold interval we suggest that this collapse was due to the incursion of warm subsurface water under the ice shelf fronting the ji ice stream as well as increased surface air temperature and sea surface temperature seasonality starting at the beginning of the yd cold interval the triggered acceleration of the land based ji and the delivery of icebergs into disko bugt potentially contributed to heinrich event 0 at the end of the yd the collapse of the ji ice stream 12 2 0 6 ka ago demonstrates that calving marine based ice margins can respond rapidly to environmental changes it provides a new benchmark for marine terminating ice stream models

paleoseismic investigations in the santa cruz mountains california implications for recurrence of large magnitude earthquakes on the san andreas fault trenching microgeomorphic mapping and tree ring analysis provide information on timing of paleoearthquakes and behavior of the san andreas fault in the santa cruz mountains at the grizzly flat site alluvial units dated at 1640 1659 a d 1679 1894 a d 1668 1893 a d and the present ground surface are displaced by a single event this was the 1906 surface rupture combined trench dates and tree ring analysis suggest that the penultimate event occurred in the mid 1600 s possibly in an interval as narrow as 1632 1659 a d there is no direct evidence in the trenches for the 1838 or 1865 earthquakes which have been proposed as occurring on this part of the fault zone in a minimum time of about 340 years only one large surface faulting event 1906 occurred at grizzly flat in contrast to previous recurrence estimates of 95 110 years for the santa cruz mountains segment comparison with dates of the penultimate san andreas earthquake at sites north of san francisco suggests that the san andreas fault between point arena and the santa cruz mountains may have failed either as a sequence of closely timed earthquakes on adjacent segments or as a single long rupture similar in length to the 1906 rupture around the mid 1600 s the 1906 coseismic geodetic slip and the late holocene geologic slip rate on the san francisco peninsula and southward are about 50 70 and 70 of their values north of san francisco respectively the slip gradient along the 1906 rupture section of the san andreas reflects partitioning of plate boundary slip onto the san gregorio sargent and other faults south of the golden gate if a mid 1600 s event ruptured the same section of the fault that failed in 1906 it supports the concept that long strike slip faults can contain master rupture segments that repeat in both length and slip distribution recognition of a persistent slip rate gradient along the northern san andreas fault and the concept of a master segment remove the requirement that lower slip sections of large events such as 1906 must fill in on a periodic basis with smaller and more frequent earthquakes

rapid rise of sea level 19 000 years ago and its global implications evidence from the irish sea basin supports the existence of an abrupt rise in sea level meltwater pulse at 19 000 years before the present b p climate records indicate a large reduction in the strength of north atlantic deep water formation and attendant cooling of the north atlantic at this time indicating a source of the meltwater pulse from one or more northern hemisphere ice sheets warming of the tropical atlantic and pacific oceans and the southern hemisphere also began at 19 000 years b p these responses identify mechanisms responsible for the propagation of deglacial climate signals to the southern hemisphere and tropics while maintaining a cold climate in the northern hemisphere

paleoseismic studies of the san francisco peninsula segment of the san andreas fault zone near woodside california a late holocene slip rate is proposed for the san francisco peninsula segment of the san andreas fault zone at the filoli center located between the town of woodside and upper crystal springs reservoir california at this site the primary trace of the san andreas fault zone traverses n35 w across the head of a large alluvial fan offsetting buried stream channel deposits one deposit with a minimum calibrated accelerator mass spectrometry ams radiocarbon age of 2070 120 years b p is offset 30 2 m yielding an average geologic slip rate of 17 4 mm yr 1 for the late holocene a stratigraphically lower channel sequence with a minimum calibrated ams radiocarbon age of 330 200 years b p is offset 4 1 0 5 m we interpret that this older sequence records both the penultimate earthquake on the peninsula segment accompanied by 1 6 0 7 m of dextral slip and the 2 5 m of slip that occurred in 1906 on the basis of radiocarbon analyses and historical descriptions we propose that the pre 1906 earthquake occurred in june 1838 our interpretations suggest that the san francisco peninsula segment of the san andreas fault zone may rupture in earthquakes of at least two magnitudes 1 a large magnitude mw 8 event with a recurrence of 250 320 years that involves the north coast san francisco peninsula and santa cruz mountains segments as occurred in 1906 and 2 a mw 7 0 7 4 1838 type event that ruptures only the san francisco peninsula segment the apparent difference in slip rate of 7 7 mm yr 1 between the north coast segment 24 3 mm yr 1 and the peninsula segment 17 4 mm yr 1 suggests a possible slip rate gradient on the northern california section of the san andreas fault

seismic moments local magnitudes and coda duration magnitudes for earthquakes in central california onscale seismograms recorded at stations in the u s geological survey s usgs central california seismic network calnet have been used to estimate the seismic moment m and local magnitude ml for earthquakes of 1 ml 4 located on the san juan bautista and parkfield sections of the san andreas fault the coyote lake section of the calaveras fault the sargent fault and near livermore these data together with m and ml estimates for 4 ml 6 earthquakes in these areas cannot be fit with a single linear log m versus ml relation rather the data are consistent with log m 1 5 ml 16 for 3 ml 6 with log m 1 2 ml 17 for 1 1 2 ml 3 1 2 and with a slope of to 1 fro 1 2 ml 1 1 2 whereas usgs coda duration magnitude md is consistent with ml for 1 1 2 ml 3 md is larger than ml at ml 1 1 2 and smaller than ml at ml 3 log m can be estimated to a precision of 0 2 for 1 md 3 1 2 earthquakes in central california by applying log m 1 2 md 17 to the md that have been routinely published by the usgs

dissolved cadmium in the southern ocean distribution speciation and relation to phosphate we report isotope dilution analyses of dissolved cadmium cd and electrochemical cd speciation measurements in the atlantic sector of the southern ocean bioavailable inorganic cd is 100 times higher in near surface waters south of the polar front compared to the subantarctic zone because of upwelling and reduced complexation by organic cd ligands to trace local changes in the relation between cd and p we examine the deviations from a linear deep water cd vs p relation cd and find that changes in cd coincide with the position of frontal systems and covary with primary productivity and total dissolved mn and fe concentrations these covariations agree with potential local changes in phytoplankton cd uptake rates resulting from differences in the availability of cd zn mn and fe a band of negative cd values is associated with formation of subantarctic mode water samw and antarctic intermediate water aaiw in contrast to samw which may export low cd p ratios from the southern ocean the cd p ratios in aaiw increase by mixing with underlying upper circumpolar deep water before being exported from the southern ocean deep waters show constant cd p ratios and both elements behave conservatively with end member mixing between deep waters of the weddell gyre the antarctic circumpolar current and inflowing north atlantic deep water overall our results support the hypothesis that the kink in the global cd vs p relation is largely caused by high cd p uptake ratios in the trace nutrient limited southern ocean

retardations in fault creep rates before local moderate earthquakes along the san andreas fault system central california records of shallow aseismic slip fault creep obtained along parts of the san andreas and calaveras faults in central california demonstrate that significant changes in creep rates often have been associated with local moderate earthquakes an immediate postearthquake increase followed by gradual long term decay back to a previous background rate is generally the most obvious earthquake effect on fault creep this phenomenon identified as aseismic afterslip usually is characterized by above average creep rates for several months to a few years in several cases minor step like movements called coseismic slip events have occurred at or near the times of mainshocks one extreme case of coseismic slip recorded at cienega winery on the san andreas fault 17 5 km southeast of san juan bautista consisted of 11 mm of sudden displacement coincident with earthquakes ofm l 5 3 andm l 5 2 that occurred 2 5 minutes apart on 9 april 1961 at least one of these shocks originated on the main fault beneath the winery creep activity subsequently stopped at the winery for 19 months then gradually returned to a nearly steady rate slightly below the previous long term average

seismicity and shear strain in the southern great basin of nevada and california this study examines the relationship between the distribution of small earthquakes ml 4 3 and mechanisms of strain accumulation and relaxation in an area with long repeat times between large events the southern great basin seismic network sgbsn region the great basin is a unique continental extensional province characterized by normal and strike slip faulting high heat flow crust of thin to normal thickness and high elevations the sgbsn is operated to provide data to address suitability issues pertaining to yucca mountain nevada which is being evaluated as a potential site for a national mined geologic nuclear waste repository suitability issues include estimation of the probability of occurrence of future damaging earthquakes the characterization of the mechanisms that drive hydrologic flow and the identification of fractures faults that might act as flow conduits or barriers this study attempts to explain the distribution of small earthquakes in terms of spatial variations in the shear strain field where strain concentrates there should be a greater number of small earthquakes strain field models are constructed under the assumption that long term fault behavior perturbs an otherwise uniform strain field these strain field models are then interpreted with regard to the regional tectonics and site suitability issues modeling results provide one possible explanation of why earthquake clusters cover regions much larger than the surface projections of any of mapped major faults clusters in a wide band along and extending northeast of the northern half of the furnace creek fault may correspond to elevated shear strains along the fault and a broad cluster in the pahranagat shear zone may be associated with shear strain arising from a distribution of smaller localized faults the relatively large number of small earthquakes in the southern and eastern portions of the nevada test site is consistent with the strain field models a minimum in shear strain at yucca mountain is predicted by all models consistent with an almost total lack of earthquakes observed there the region to the west of the death valley furnace creek fault system the portion of the study area with the most active deformation but few small earthquakes is an area of low shear strain a possible reason for this is that the fault configuration in the area is optimal for accommodating regional deformation via large earthquakes or creep while there is also a relative lack of earthquakes at yucca mountain this may be indicative of a lack of accumulating strain energy and thus a lower potential for a large earthquake

marine 14c reservoir ages for 19th century whales and molluscs from the north atlantic abstract in order to compare radiocarbon dates on marine and terrestrial samples the former have to be corrected for a reservoir age we present reservoir ages from dating 21 whales collected 1860 1901 and recalculating dates of 23 molluscs collected 1857 1926 most of the whales were caught along the coast of norway but one is from france and one from iceland we assume the former mainly lived in the north and equatorial atlantic and in the norwegian sea whales feed only on pelagic organisms and will provide the reservoir age for the open ocean surface water however they travel long distances and will integrate the reservoir ages of the different water masses along their way molluscs dated from norway spitsbergen and arctic canada are stationary and monitor the sea water passing their dwelling site but some also take up carbon from particulate food or sediment pore water coastal water also often contains some continental carbon we present two different views on how to analyze and interpret the data mangerud recommends to use reservoir ages based on a combination of the whale and mollusc dates i e 380 30 and 360 30 yr relative to intcal04 and british oak respectively and a r value of 20 30 for the surface water in the n atlantic and norwegian sea bondevik and gulliksen maintain that the reservoir age and r along the norwegian coast is latitude dependant with r values increasing from 3 22 in the south to 105 24 at spitsbergen whales reflecting north atlantic open ocean surface water have lower r 7 11 than most molluscs

silicon and zinc biogeochemical cycles coupled through the southern ocean zinc is vital for the physiology of oceanic phytoplankton the striking similarity of the depth profiles of zinc to those of silicate suggests that the uptake of both elements into the opaline frustules of diatoms and their regeneration from these frustules should be coupled however the zinc content of diatom opal is negligible and zinc is taken up into and regenerated from the organic parts of diatom cells thus since opaline frustules dissolve deep in the water column while organic material is regenerated in the shallow subsurface ocean there is little reason to expect the observed close similarity between zinc and silicate and the dissimilarity between zinc and phosphate here we combine observations with simulations using a three dimensional model of ocean circulation and biogeochemistry to show that the coupled distribution of zinc and silicate as well as the decoupling of zinc and phosphate can arise in the absence of mechanistic links between the uptake of zinc and silicate and despite contrasting regeneration length scales our simulations indicate that the oceanic zinc distribution is in fact a natural result of the interaction between ocean biogeochemistry and the physical circulation through the southern ocean hub our analysis demonstrates the importance of uptake stoichiometry in controlling ocean biogeochemistry and the utility of global scale elemental covariation in the ocean in understanding these controls zinc and silicon distributions co vary in much of the global oceans observations and numerical modelling suggest that this co variation can arise in the absence of mechanistic links between the uptake of zinc and silicate

asynchronous response of marine terminating outlet glaciers during deglaciation of the fennoscandian ice sheet this is the accepted manuscript version published version is available at http dx doi org 10 1130 g35299 1

biogeochemical cycling of dissolved zinc along the geotraces south atlantic transect ga10 at 40 s the biogeochemical cycle of zinc zn in the south atlantic at 40 s was investigated as part of the uk geotraces program to date there is little understanding of the supply of zn an essential requirement for phytoplankton growth to this highly productive region vertical zn profiles displayed nutrient like distributions with distinct gradients associated with the water masses present surface zn concentrations are among the lowest reported for the world s oceans 2 0 97 n 460 our results suggest that the use of a global zn si relationship would lead to an underestimation of dissolved zn in deeper waters of the south atlantic by utilizing si and a new tracer zn our data indicate that the preferential removal of zn in the southern ocean prevented a direct return path for dissolved zn to the surface waters of the south atlantic at 40 s and potentially the thermocline waters of the south atlantic subtropical gyre the importance of zn for phytoplankton growth was evaluated using the zn soluble reactive phosphorus srp relationship we hypothesize that the low zn concentrations in the south atlantic may select for phytoplankton cells with a lower zn requirement in addition a much deeper kink at 500m in the zn srp ratio was observed compared to other oceanic regions key points dissolved zinc biogeochemical cycle investigated in the south atlantic ocean 2014 american geophysical union all rights reserved

postseismic strain following the 1989 loma prieta earthquake from gps and leveling measurements postseismic deformation in the 5 years following the 1989 loma prieta earthquake has been measured with the global positioning system and precise leveling postearthquake velocities at distances greater than 20 km from the coseismic rupture are not significantly different from those observed in the 20 years prior to the earthquake however velocities at stations within 20 km of the rupture exceed preearthquake rates and exhibit unanticipated contraction normal to the strike of the san andreas fault system a combination of forward modeling and nonlinear optimization suggests that the observed postseismic deformations were caused by aseismic oblique reverse slip averaging 2 9 cm yr on the san andreas fault and or the loma prieta rupture zone and 2 4 cm yr reverse slip along a buried fault within the foothills thrust belt the best fitting sources of postseismic deformation are all located at depths of less than 15 km we find no evidence for accelerated flow or shear below the loma prieta rupture in the first 5 years following the earthquake the inferred postseismic slip is likely to have been caused by the coseismic stress change updip of the 1989 rupture

changes in north atlantic radiocarbon reservoir ages during the allerod and younger dryas estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late quaternary climate we radiocarbon dated marine shells and terrestrial plant remains deposited in two bays on norway s west coast between 11 000 and 14 000 years ago a time of large and abrupt climatic changes that included the younger dryas yd cold episode the radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early yd stabilized for 900 years and dropped by 300 years within a century across the yd holocene transition

middle and late weichselian devensian glaciation history of south western norway north sea and eastern uk data from eastern england scotland the northern north sea and western norway have been compiled in order to outline our current knowledge of the middle and late weichselian glacial history of this region radiometric dates and their geological context from key sites in the region are presented and discussed based on the available information the following conclusions can be made i prior to 39 cal ka and most likely after ca 50 cal ka scotland and southern norway were extensively glaciated most likely the central north sea was not glaciated at this time and grounded ice did not reach the shelf edge ii during the time interval between 29 and 39 ka periods with ameliorated climate including the alesund sandnes and tolsta interstadials alternated with periods of restricted glaciation in scotland and western norway iii between 29 and 25 ka maximum weichselian glaciation of the region occurred with the fennoscandian and british ice sheets coalescing in the central north sea iv decoupling of the ice sheets had occurred at 25 ka with development of a marine embayment in the northern north sea v between 22 and 19 ka glacial ice expanded westwards from scandinavia onto the north sea plateau in the tampen readvance vi the last major expansion of glacial ice in the offshore areas was between 17 5 and 15 5 ka at this time ice expanded in the north western part of the region onto the maloy plateau from norway and across caithness and orkney and to east of shetland from the moray firth the norwegian channel ice stream ncis which drained major parts of the south western fennoscandian ice sheet was active at several occasions between 29 and 18 ka

near source modeling of the loma prieta earthquake evidence for heterogeneous slip and implications for earthquake hazard i have analyzed records from 20 strong motion instruments that recorded the 1989 loma prieta earthquake ml 6 9 to determine the spatial and temporal distribution of slip using a tomographic back projection technique i find that the earthquake ruptured bilaterally at approximately 80 of the local shear wave velocity over a distance of slightly more than 30 km from 13 km northwest to 20 km southeast of the hypocenter slip within the rupture zone was highly variable both in magnitude and direction slip at the hypocenter and immediately up dip was relatively low about 1 m there were two main areas of concentrated slip one centered 7 km northwest of the hypocenter at a depth of 14 km and the other centered 6 km southeast of the hypocenter at a depth of 12 km peak slip amplitude on these high slip patches exceeded 4 5 m a surprising aspect of the rupture model is that rake varies from being predominately strike slip to the southeast of the hypocenter to being predominately reverse slip to the northwest despite this variation in rake the average rake determined from the strong motion data is in agreement with that determined teleseismically there is a correlation between areas of high slip and areas of low aftershock activity a simple model to explain this observation is that the areas of high slip are also areas of high strength which slip only during infrequent large mainshocks other areas of the fault are weaker and may slip both seismically and aseismically most of the slip in the loma prieta earthquake occurred between 9 and 16 km depth on a structure that dips to the southwest and runs underneath the surface trace of the san andreas fault at a depth of 8 to 10 km this observation complicates the assessment of seismic hazard on the southern santa cruz mountains segment of the san andreas fault

geodetic measurement of crustal deformation on the san andreas hayward and calaveras faults near san francisco california analysis of a geodetic network of 115 lines crossing the san andreas hayward and calaveras faults in the vicinity of san francisco bay and measured repeatedly between 1970 and 1980 has revealed details about the accommodation of relative plate motion in this area the most striking result is that the deformation is not uniformly distributed across the area in the east bay along the hayward and calaveras faults all motion appears to take place as slip directly on the fault with no accumulation of strain in the adjacent crust on both the calaveras and the hayward faults the rate obtained for the 1970 to 1980 period agrees with geologic rates spanning a few million years and with creep rates spanning a few decades the hayward fault slip rate is 7 1 mm yr the calaveras fault slip rate is 7 1 mm yr with perhaps half of this slip distributed across a zone a few kilometers wide probably as inelastic deformation of weak near surface material the absence of strain accumulation in the east bay is surprising since the hayward and calaveras faults have been the site of large earthquakes in the past a block located east of the calaveras fault and south of the las positas fault has been rotating clockwise at a rate of 0 3 0 1 rad yr with very little internal deformation along the san francisco peninsula no detectable slip occurs less than 1 5 mm yr at the surface but appreciable strain is accumulating near fault shear strain rates are 0 6 0 1 strain yr engineering with direction n47 w 9 the slip rate near the san andreas fault is 12 2 3 9 mm yr distributed across a broad zone the relative motion across the whole region during the period 1970 1980 is 32 1 7 4 mm yr supplement available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j81 011 1 00 payment must accompany order

new boundary conditions for the west antarctic ice sheet subglacial topography beneath pine island glacier 1 predictions about future changes in the amundsen sea sector of the west antarctic ice sheet wais have been hampered by poorly known subglacial topography extensive airborne survey has allowed us to derive improved subglacial topography for the pine island glacier basin the trunk of this glacier lies in a narrow 250 km long 500 m deep sub glacial trough suggesting a long lived and constrained ice stream two tributaries lie in similar troughs others lie in less defined shallower troughs the lower basin of the glacier is surrounded by bedrock which after deglaciation and isostatic rebound could rise above sea level this feature would impede ice sheet collapse initiated near the grounding line of this glacier and prevent its progress into the deepest portions of wais the inland slope of the bed beneath the trunk of the glacier however confirms potential instability of the lower basin containing sufficient ice to raise global sea by 24 cm

ice flow patterns and precise timing of ice sheet retreat across a dissected fjord landscape in western norway abstract we reconstruct patterns of ice flow and retreat of the southwestern scandinavian ice sheet from 2900 field observations of glacial striae and elevation measurements of 60 ice marginal deltas from a high resolution lidar dem during the last glacial maximum ice flow was towards the west across the entire area including across several hundred meter deep north south oriented fjords during deglaciation ice flow adjusted to topography and the dominant flow direction switched towards the south west we use a shoreline diagram constructed from relative sea level curves to establish the age of each delta which allows us to constrain the timing of retreat with almost decadal precision rapid ice sheet retreat commenced at the onset of the holocene at 11 600 cal years bp retreat rates were 160 m a 1 in the deepest fjords 60 80 m a 1 in shallower fjords and even slower for land terminating margins the fastest retreat rates 240 m a 1 and 340 m a 1 were experienced in the largest fjords hardangerfjorden and sognefjorden which border the study area to the south and north crosscutting glacial striae indicate that calving bays developed during retreat along the widest fjords the combination of complex fjord topography with fast ice margin retreat by iceberg calving led to isolation of ice remnants on islands and peninsulas a process that accelerated the overall rate of deglaciation ice margin retreat paused between 11 300 11 100 cal years bp probably due to cooling during the preboreal oscillation

glacigenic debris flows on the north sea trough mouth fan during ice stream maxima abstract numerous short sediment cores which penetrate through the glacimarine section and into glacigenic debris flow debrites gdfs on the north sea fan are investigated the sampled gdfs represent the uppermost of several sequences of these stacked bodies many hundreds of metres thick the gdfs occurred over slopes from 0 3 to 0 7 and examples are found from the shelf break at the mouth of the norwegian channel to the norway basin floor 300 km distant the gdf diamicts are structureless and homogeneous in terms of grain size magnetic susceptibility nrm bulk density water carbonate foraminiferal and rock fragment content this applies both from gdf to gdf across the fan and in a proximal distal sense comparison of the investigated lithologic parameters with weichselian till from a borehole in the norwegian channel 200 km up ice shows striking similarity to the gdf debrites ams 14c dates at the gdf glacimarine contact and stratigraphic relationships indicate voluminous deposition before 18 ka continuing possibly uninterrupted until ca 16 ka and a final phase halting just before 15 ka when the norwegian channel became ice free this chronology the comparable lithologic character between till and gdf debrites and a seismic continuity confirms inferences that the gdfs are directly associated with glacial ice at the shelf break the glacial efflux has not been subject to subsequent sorting and the homogeneity of the gdf is thought to reflect thorough mixing in a deforming till layer beneath a fast flowing ice stream the glacimarine section subsequent to gdfs shows no indications of turbidity flow observations are compatible with a slow non disintegrating cohesive plug flow transport mechanism with little sediment water interaction on the upper surface minor distal differentiation might reflect a change in flow process deposition on the fan margins from water borne glacimarine processes simultaneous with gdf deposition is limited

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

a simple law for ice shelf calving a major problem for ice sheet models is that no physically based law for the calving process has been established comparison across a diverse set of ice shelves demonstrates that iceberg calving increases with the along flow spreading rate of a shelf this relation suggests that frictional buttressing loss which increases spreading also leads to shelf retreat a process known to accelerate ice sheet flow and contribute to sea level rise

winter and summer distributions of copper zinc and nickel along the international geotraces section gipy05 insights into deep winter mixing abstract first measurements of labile dissolved copper ldcu and dissolved zinc dzn and nickel dni in the atlantic sector of the southern ocean in winter are compared with summer data at reoccupied stations in order to better understand the winter reset state and supply of these trace metals to support productivity in summer vertical profiles of zinc behaved similarly to silicate si and increased from sub nanomolar surface concentrations to 8 nmol kg 1 in bottom waters copper profiles also resembled si and were typically 1 nmol kg 1 in surface waters and increased to 3 nmol kg 1 at depth first summer nickel data reported from this transect displayed comparatively higher surface concentrations of 4 6 nmol kg 1 increasing more rapidly to local intermediate depth maximums between 6 5 and 7 0 nmol kg 1 similar to phosphate po4 trace metal seasonality was most apparent in the mixed layer where the average of winter concentrations within the mixed layer exceeded summer values by approximately 0 2 nmol kg 1 for ldcu 1 2 nmol kg 1 for dzn and 0 3 nmol kg 1 for dni owing to low utilization under unfavourable growth conditions for phytoplankton in an effort to estimate the winter reserve two scenarios were considered scenario 1 accounted for in situ mixed layer depths mld where the winter reserve inventory was calculated by subtracting the summer depth integrated metal inventory surface to summer mld from the winter equivalent surface to winter mld scenario 2 assumed a constant mixed layer taken as the depth of the maximum winter mixed layer where summer depth integrated metal inventories surface to maximum winter mld were subtracted from the winter equivalents surface to maximum winter mld results for scenario 1 were predominantly dependent on the mixed layer depth which varied spatially and seasonally scenario 2 showed a southwards increase in the winter reserve inventory suggesting a greater role for entrainment at higher latitudes in this region this is however heavily dependent on other physical processes controlling vertical trace metal supply e g diapycnal diffusion ekman upwelling downwelling zinc r2 0 75 and copper r2 0 73 were strongly correlated with si throughout the study implicating diatoms as strong controllers of their biogeochemical cycling nickel was more strongly correlated with po4 in the upper water column r2 0 75 as compared to the whole water column r2 0 52 while in the deep ocean nickel appears to correlate with si although more deep ocean data is needed to confirm this trace metal to major nutrient ratios were higher in winter suggesting reduced micronutrient requirement relative to macronutrients under stressed but low productivity conditions this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

geodetic estimate of coseismic slip during the 1989 loma prieta california earthquake offsets in the relative positions of geodetic stations resulting from the loma prieta earthquake can be explained with a dislocation model that includes buried oblique slip on a rupture surface extending 37 km along the strike of the san andreas fault dipping 70 degree to the sw and extending from a depth of about 5 to 17 5 km assuming uniform slip on a rectangular surface the mean values for a range of reasonable fault geometries are 1 6 plus minus 0 3 m right lateral strike slip and 1 2 plus minus 0 3 m reverse slip slip on an adjacent extension of the rupture to the southeast recorded in the aftershock sequence is not well constrained by the geodetic data the geodetic data clearly preclude rupture extending near the surface

a 10be chronology of south western scandinavian ice sheet history during the lateglacial period we present 34 new cosmogenic 10be exposure ages that constrain the lateglacial bolling preboreal history of the scandinavian ice sheet in the lysefjorden region south western norway we find that the classical lysefjorden moraines earlier thought to be entirely of younger dryas age encompass three adjacent moraines attributed to at least two ice sheet advances of distinctly different ages the 10be age of the outermost moraine 14 0 0 6 ka n 4 suggests that the first advance is of older dryas age the innermost moraine is at least 2000 years younger and was deposited near the end of the younger dryas 11 4 0 4 ka n 7 after abandonment of the innermost lysefjorden moraine the ice front receded quickly towards the head of the fjord where recession was interrupted by an advance that deposited the trollgaren moraine at 11 3 0 9 ka n 5 10be ages from the inboard side of the trollgaren moraine suggest final retreat by 10 7 0 3 ka n 7 the late culmination of the younger dryas advance contrasts with other sectors of the scandinavian ice sheet where the margin appears to have culminated earlier during the younger dryas stadial followed by retreat during the middle and late part of the younger dryas

rapid early holocene retreat of a laurentide outlet glacier through an arctic fjord marine terminating outlet glaciers control the stability of ice sheets exposure ages and radiocarbon dates show that an arctic outlet glacier of the laurentide ice sheet rapidly retreated about 9 500 years ago and imply strong feedbacks between bathymetry and ice movement

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

erratum late glacial and holocene 10be production rates for western norway 1 calculation of the sea level high latitude production rate based on the samples from the herdla halsnoy younger dryas end moraine required accounting for the isostatic rebound of the site following deglaciation lohne et al 2007 in the process of calculating exposure ages of samples from nearby sites it was realized that the original calibration of the production rates from halsnoy were calculated using a correction based on the relative sea level history 70m maximum plus the eustatic sea level history 50m at maximum i e that the amount of isostatic depression had been over corrected sea level high latitude be production rates based on the correct relative sea level history are presented below in a corrected version of table 2 2 in the original publication the combined production rates were determined using a chi squared minimization based on the data from both calibration sites however because the two studied sites have significantly different ages halsnoy 11650 100 and oldedalen 6070 111 and therefore integrate production over different lengths of time it is inappropriate to determine a sea level high latitude production rate for the entire data set using the chi squared minimization instead the arithmetic mean of the production rates from the two sites is the more appropriate average production rate we present in the corrected table 2 below both the updated production rate values for the samples from halsnoy and average production rates using the arithmetic mean and standard deviation of the production rates from the two sites we apologize for any inconvenience caused references

the distribution of dissolved zinc in the atlantic sector of the southern ocean the distribution of dissolved zinc zn was investigated in the atlantic sector of the southern ocean in the austral autumn of 2008 as part of the ipy geotraces expedition zero drake research focused on transects across the major frontal systems along the zero meridian and across the drake passage there was a strong gradient in surface zinc concentrations observed across the antarctic polar front along both transects and high zinc levels were found in surface waters throughout the southern ocean vertical profiles for dissolved zinc showed the presence of local minima and maxima in the upper 200 m consistent with significant uptake by phytoplankton and release by zooplankton grazing respectively highest deep water zinc concentrations were found in the centre of the weddell gyre associated with central intermediate water ciw a water mass which is depleted in o2 elevated in co2 and is regionally a cfc minimum our data suggests that the remineralization of sinking particles is a key control on the distribution of zn in the southern ocean disappearance ratios of zinc to phosphate zn p in the upper water column increased southwards along both transects and based on laboratory studies they suggest slower growth rates of phytoplankton due to iron or light limitation zinc and silicate were strongly correlated throughout the study region but the disappearance ratio zn si was relatively uniform overall except for the region close to the ice edge on the zero meridian

collapse of marine based outlet glaciers from the scandinavian ice sheet abstract we present a reconstruction of the timing and retreat rates of more than 2000 m thick younger dryas yd fjord glaciers in western norway using a detailed chronology of 10 be exposure ages from lateral moraines and 14 c dated end moraines a primary conclusion is that ice margins retreated up the 120 170 km long fjords at mean rates of 240 340 m yr 1 during the early holocene we further show that part of the south western sector of the scandinavian ice sheet collapsed in two distinct steps the first step occurred between 19 5 and 18 5 ka bp as break up of the norwegian channel ice stream which drained the ice sheet during the last glacial maximum lgm the second step was the rapid retreat up the fjords mentioned above dated to 11 6 11 1 ka bp during the intervening 7000 years no net retreat occurred despite oscillations of the ice margin this stepwise ice margin retreat strongly contrasts with the more monotonic decay of the ice sheet as a whole indicating that water depths set the pace for climate triggered ice margin retreat in this part of the ice sheet calving and melting of marine margins has dominated mass loss from modern ice sheets in recent decades however the mechanisms and long term 100 1000 yr rate of ice front retreat is less certain and empirical examples such as those given here may help in developing better numerical models

on the relationship between fronts of the antarctic circumpolar current and surface chlorophyll concentrations in the southern ocean 1 we reexamine the relationship between circulation bathymetry and surface chlorophyll in the southern ocean using new high resolution maps of the frontal structure of the antarctic circumpolar current acc derived from satellite altimetry the maps reveal that the acc consists of multiple filaments or jets by averaging surface chlorophyll measurements along streamlines we show that the fronts define the limits of zones with similar concentrations and seasonality of surface chlorophyll the overall pattern of surface chlorophyll is consistent with strongest upwelling of nutrient rich deep water south of the polar front pf however the distribution of chlorophyll in the southern ocean is concentrated in a number of persistent blooms observed downstream of islands and bathymetric features in contrast to previous studies we find little evidence that the fronts of the acc are associated with enhanced productivity at least where the fronts are distant from topography rather we find that most regions of elevated chlorophyll in the open southern ocean can be explained by upwelling of nutrients both macronutrients and micronutrients where the acc interacts with topography followed by downstream advection the upwelling is shown to be the consequence of the bottom pressure torque established by the large scale flow rather than being due to small scale instabilities of the jets the interaction of the flow with the topography therefore establishes both the large scale dynamical balance of the acc and determines the productivity of the open southern ocean

new boundary conditions for the west antarctic ice sheet subglacial topography of the thwaites and smith glacier catchments airborne radar sounding over the thwaites glacier tg catchment and its surroundings provides the first comprehensive view of subglacial topography in this dynamic part of the west antarctic ice sheet wais and reveals that tg is underlain by a single broad basin fed by a dendritic pattern of valleys while smith glacier lies within an extremely deep narrow trench subglacial topography in the tg catchment slopes inland from a broad low relief coastal sill to the thickest ice of the wais and makes deep connections to both pine island glacier and the ross sea embayment enabling dynamic interactions across the wais during deglaciation simple isostatic rebound modeling shows that most of this landscape would be submarine after deglaciation aside from an island chain near the present day ross amundsen ice divide the lack of topographic confinement along tg s eastern margin implies that it may continue to widen in response to grounding line retreat

coupled response of the late glacial climatic shifts of northwest europe reflected in greenland ice cores evidence from the northern north sea the climatic regimes of the land areas adjacent to the north sea are controlled by the influx of atlantic water north of the british isles and into the north sea a high resolution record from the norwegian channel off western norway covering the past 15 ka 14 c shows that prior to the younger dryas there were three periods of sea surface conditions there similar to those of the present interspersed with arctic conditions these changes corresponding to an increase of approx 5 c in summer sea surface temperatures took place on the scale of

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

shallow remineralization in the weddell gyre 1 the region influenced by the polar front in the southern ocean is characterized by relatively high productivity which is mirrored in strong depletions of 234th in the surface water a good tracer of export production and by high accumulation rates on the underlying seabed farther south the weddell sea is generally considered a low productivity region with very low export fluxes this finding is based on satellite observations sediment accumulation rates trap deployments and phytoplankton distribution if this would be true 234th should be close to equilibrium with its parent however in a series of high resolution transects of 234th 238u across the antarctic circumpolar current acc 234th was found to be depleted by 10 15 throughout the clear weddell gyre only to reach equilibrium in sea ice covered regions of the coastal zone vertical profiles showed that the depletion was limited to the upper mixed layer and was balanced by an enrichment of similar magnitude at 100 250m depth this implies that the export of particles below 250 m is negligible such shallow remineralization is in line with the discrepancies between biogenic silica production rates and sediment trap data observed in the weddell and ross seas these observations in the weddell sea are fully consistent with our inverse modeling results for both organic carbon and opal and they are not inconsistent with tco2 and oxygen sections that show a tco2 enriched oxygen reduced shallow subsurface layer this blue ocean characterized by upwelling of co2 enriched deep waters supports sufficient productivity to be a net sink for co2 to abyssal depths hoppema et al 1999 no record of this productivity and export is stored in the underlying sediment which has important palaeoceanographic consequences

timing of the younger dryas glacial maximum in western norway this study precisely constrains the timing of the younger dryas yd glacial maximum in south western norway by utilizing sediment records from lake basins two of the basins located on the distal side of the mapped herdla halsnoy moraine received meltwater directly from the ice sheet only when the ice margin reached its maximum extent during the yd in the cores the ice maximum is represented by well defined units with meltwater deposits dominantly laminated silt plant macrofossils in the sediment sequences are common and we obtained 18 radiocarbon ages from one of the cores by applying bayesian age depth modelling we obtained a precise date for this meltwater event and thereby also for the timing of the yd glacial maximum we conclude that the ice sheet advance culminated at the halsnoy moraine at 11 760 120 cal a bp and that the ice margin stayed in this position for 170 120 years the subsequent retreat started at 11 590 100 cal a bp i e close to the yd holocene boundary withdrawal was probably triggered by abrupt climatic warming at this time copyright 2011 john wiley sons ltd

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

block versus continuum deformation in the western united states abstract the relative role of block versus continuum deformation of continental lithosphere is a current subject of debate continuous deformation is suggested by distributed seismicity at continental plate margins and by cumulative seismic moment sums which yield slip estimates that are less than estimates from plate motion studies in contrast block models are favored by geologic studies of displacement in places like asia a problem in this debate is a lack of data from which unequivocal conclusions may be reached in this paper we apply the techniques of study used in regions such as the alpine himalayan belt to an area with a wealth of instrumental data the western united states by comparing plate rates to seismic moment release rates and assuming a typical seismogenic layer thickness of 15 km it appears that since 1850 about 60 of the pacific north america motion across the plate boundary in california and nevada has occurred seismically and 40 aseismically the san francisco bay area shows similar partitioning between seismic and aseismic deformation and it can be shown that within the seismogenic depth range aseismic deformation is concentrated near the surface and at depth in some cases this deformation can be located on creeping surface faults but elsewhere it is spread over a several kilometer wide zone adjacent to the fault these superficial creeping deformation zones may be responsible for the palaeomagnetic rotations that have been ascribed elsewhere to the surface expression of continuum deformation in the lithosphere our results support the dominant role of non continuum deformation processes with the implication that deformation localization by strain softening must occur in the lower crust and probably the upper mantle our conclusions apply only to the regions where the data are good and even within the western united states i e the basin and range deformation styles remain poorly resolved nonetheless we maintain that block motion is the deformation style of choice for those continental regions where the data are best

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

sea level fluctuations imply that the younger dryas ice sheet expansion in western norway commenced during the allerod after the first emergence following deglaciation relative sea level rose by 10 m in western norway and culminated late in the younger dryas yd the relative sea level history reconstructed by dating deposits in isolation basins shows a sea level low stand between 13 640 and 13 080 cal yr bp a 10 m sea level rise between 13 080 and 11 790 cal yr bp and a sea level high stand between 11 790 and 11 550 cal yr bp shortly after the yd holocene boundary sea level fell abruptly by 37 m the shorelines formed during the sea level low stand in the mid allerod and during the sea level high stand in the yd have almost parallel tilts with a gradient of 1 3 m km 1 indicating that hardly any isostatic movement has taken place during this period of sea level rise we conclude that the transgression was caused by the major re advance of the scandinavian ice sheet that took place in western norway during the lateglacial the extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea our results show that the crust responded to the increased load well before the yd starting 12 900 cal yr bp with a sea level low stand at 13 640 cal yr bp and the subsequent yd transgression starting at 13 080 cal yr bp thus we conclude that the so called yd ice sheet advance in western norway started during the allerod possibly more than 600 years before the allerod yd transition r 2007 elsevier ltd all rights reserved

dissolved manganese in the atlantic sector of the southern ocean the first comprehensive dataset 492 samples of dissolved mn in the southern ocean shows extremely low values of 0 04 up to 0 64 nm in the surface waters and a subsurface maximum with an average concentration of 0 31 nm n 20 s d 0 08 nm the low mn in surface waters correlates well with the nutrients po4 and no3 and moderately well with si oh 4 and fluorescence furthermore elevated concentrations of mn in the surface layer coincide with elevated fe and light transmission and decreased export th 234 u 238 deficiency and fluorescence it appears that mn is a factor of importance in partly explaining the hnlc conditions in the southern ocean in conjunction with significant controls by the combination of fe limitation and light limitation no input of mn from the continental margins was observed this is ascribed to the protruding continental ice sheet that covers the shelf and shuts down the usual biological production microbial breakdown and sedimentary geochemical cycling the low concentrations of mn in the deep ocean basins 0 07 0 23 nm were quite uniform but some elevations were observed the highest deep concentrations of mn were observed at the bouvet triple junction region and coincided with high concentrations of fe and are deemed to be from hydrothermal input the deep basins on both sides of the ridge were affected by this input in the deep weddell basin the input of weddell sea bottom water appears to be the source of the slightly elevated concentrations of mn in this water layer c 2010 elsevier ltd all rights reserved

on the origin of the marine zinc silicon correlation abstract the close linear correlation between the distributions of dissolved zinc zn and silicon si in seawater has puzzled chemical oceanographers since its discovery almost forty years ago due to the apparent lack of a mechanism for coupling these two nutrient elements recent research has shown that such a correlation can be produced in an ocean model without any explicit coupling between zn and si via the export of zn rich biogenic particles in the southern ocean consistent with the observation of elevated zn quotas in southern ocean diatoms here we investigate the physical and biological mechanisms by which southern ocean uptake and export control the large scale marine zn distribution using suites of sensitivity simulations in an ocean general circulation model ogcm and a box model ensemble these simulations focus on the sensitivity of the zn distribution to the stoichiometry of zn uptake relative to phosphate po4 drawing directly on observations in culture our analysis reveals that ogcm model variants that produce a well defined step between relatively constant high zn po4 uptake ratios in the southern ocean and low zn po4 ratios at lower latitudes fare best in reproducing the marine zn si correlation at both the global and the regional southern ocean scale suggesting the presence of distinct zn biogeochemical regimes in the high and low latitude oceans that may relate to differences in physiology ecology or micro nutrient status furthermore a study of the systematics of both the box model and the ogcm reveals that regional southern ocean zn uptake exerts control over the global zn distribution via its modulation of the biogeochemical characteristics of the surface southern ocean specifically model variants with elevated southern ocean zn po4 uptake ratios produce near complete zn depletion in the si poor surface subantarctic zone where upper ocean water masses with key roles in the global oceanic circulation are formed by setting the main preformed covariation trend within the ocean interior the subduction of these zn and si poor water masses produces a close correlation between the zn and si distributions that is barely altered by their differential remineralisation during low latitude cycling we speculate that analogous processes in the high latitude oceans may operate for other trace metal micronutrients as well splitting the ocean into two fundamentally different biogeochemical and thus biogeographic regimes

long term seismic potential of the san andreas fault southeast of san francisco california the long term decade or longer seismic potential of the peninsular san andreas fault the 125 km long segment southeast of san francisco has been assessed by comparing the slip accompanying the 1906 mw 7 7 earthquake with the amount of this slip deficit made up since 1906 of particular importance is the longstanding factor of 2 inconsistency between 1906 surface offsets 1 5 m and geodetically determined coseismic slip 2 7 m on the southern 90 km of the peninsular san andreas in reexamining this issue we find that the discrepancy cannot be attributed to either large observational uncertainties in the geodetic data or shortcomings in fault modeling rather the problem lies in the complexity of this 90 km long fault reach where the san andreas trend changes by 6 the zone of recent deformation is 0 5 2 km wide and much of the fault is heavily vegetated and inaccessible farther northwest on the 1906 rupture where the fault geometry is much simpler evidence from deformed fences shows that right lateral coseismic slip was commonly distributed across a zone 20 600 m wide with only about 70 of the total slip occurring at the main fault trace the general importance of distributed coseismic deformation and the evidence for fault zone complexity indicate that the best estimate of 1906 slip on this 90 km fault segment is the geodetically constrained value of 2 6 0 2 m farther northwest on the peninsular san andreas the coseismic slip ranges from 3 4 to 4 4 m and geodetic slip and surface offsets show considerably better agreement following previous work we have assessed the risk posed to the southern peninsular san andreas by two broad classes of earthquakes these appraisals use the geodetic slip distribution apply a long term slip rate of 15 mm yr suggested by geologic and geodetic studies and assume the approximate correctness of the time predictable recurrence model the possibility of an m 6 1 2 earthquake on the 30 km long segment northwest of san juan bautista cannot be completely precluded but the evidence bearing on its likelihood is contradictory in contrast with several previous assessments we find that the risk of an earthquake of m 7 rupturing the southern 90 km of the peninsular san andreas during the next several decades is quite low

lateglacial and early holocene palaeoclimatic reconstruction based on glacier fluctuations and equilibrium line altitudes at northern folgefonna hardanger western norway northern folgefonna c 23 km 2 is a nearly circular maritime ice cap located on the folgefonna peninsula in hardanger western norway by combining the position of marginal mor aines with ams radiocarbon dated glacier meltwater induced sediments in proglacial lakes draining northern folgefonna a continuous high resolution record of variations in glacier size and equili brium line altitudes elas during the lateglacial and early holocene has been obtained after the termination of the younger dryas c 11 500 cal yr bp a short lived 100 150 years climatically induced glacier readvance termed the jondal event 1 occurred within the preboreal oscillation pbo c 11 100 cal yr bp bracketed to 10 550 10 450 cal yr bp a second glacier readvance is named the jondal event 2 a third readvance occurred about 10 000 cal yr bp and corresponds with the erdalen event 1 recorded at jostedalsbreen an exponential relationship between mean solid winter precipitation and ablation season temperature at the ela of norwegian glaciers is used to reconstruct former variations in winter precipitation based on the corresponding ela and an indepen dent proxy for summer temperature compared to the present the younger dryas was much colder and drier the jondal event 1 pbo was colder and somewhat drier and the jondal event 2 was much wetter the erdalen event 1 started as rather dry and terminated as somewhat wetter varia tions in glacier magnitude elas and corresponding palaeoclimatic reconstructions at northern folge fonna suggest that low altitude cirque glaciers lowest altitude of marginal moraines 290 m in the area existed for the last time during the younger dryas these low altitude cirque glaciers of sug gested younger dryas age do not fit into the previous reconstructions of the younger dryas ice sheet in hardanger copyright 2005 john wiley sons ltd

high mixing rates in the abyssal southern ocean mixing of water masses from the deep ocean to the layers above can be estimated from considerations of continuity in the global ocean overturning circulation but averaged over ocean basins diffusivity has been observed to be too small to account for the global upward flux of water and high mixing intensities have only been found in the restricted areas close to sills and narrow gaps here we present observations from the scotia sea a deep ocean basin between the antarctic peninsula and the tip of south america showing a high intensity of mixing that is unprecedented over such a large area using a budget calculation over the whole basin we find a diffusivity of 39 plus minus 10 x 104 m2 s 1 averaged over an area of 7 x 105 km2 the scotia sea is a basin with a rough topography situated just east of the drake passage where the strong flow of the antarctic circumpolar current is constricted in width the high basin wide mixing intensity in this area of the southern ocean may help resolve the question of where the abyssal water masses are mixed towards the surface

laminated sediments preceding heinrich event 1 in the northern north sea and southern norwegian sea origin processes and regional linkage abstract rapidly deposited laminated sediments dated between 18 and 21 cal ka bp have been observed at several core locations in the northern north sea and the southern norwegian sea sedimentation rates range from 20 cm ka up to 2000 cm ka compared to a normal background sedimentation rate in the area of 5 10 cm ka dropstones in situ paired bivalves and grain size distribution indicate a hemipelagic origin for the laminae in core md99 2291 from the upper continental slope of southern norway ams radiocarbon dating and cyclic changes in the number of planktonic foraminifera and lithological parameters suggest that the laminations in the core are annual varves the laminated sediments are interpreted to be suspension plume deposits and two phases of plume deposition have been dated to 21 5 and 18 6 cal ka bp large fluxes of meltwater were generated during this period as reflected in oxygen and carbon isotopes records from cores in the area the meltwater and the laminated plume deposits are interpreted to be associated with the presence and disintegration of the norwegian channel ice stream observations from other regions demonstrate that laminated high rate deposition is very widespread on glaciated continental margins around 18 6 cal ka bp increases in sediment fluxes also occurred on the barra fan the north sea fan the lofoten contourite drift and the svalbard margin preceding increased sediment and meltwater fluxes on the greenland margin and the labrador sea associated with heinrich event 1 warm water inflow to the norwegian sea together with rising sea level probably triggered the destabilisation of the ice streams of the fennoscandian ice sheet while a similar response of the laurentide ice sheet was delayed by 500 1000 yr

re evaluation of several large historic earthquakes in the vicinity of the loma prieta and peninsular segments of the san andreas fault california abstract the size and location of several of the largest 19th century earthquakes in the san francisco bay area including the june 1838 8 october 1865 21 october 1868 and 24 april 1890 events are re evaluated by comparing these historic events to several modern events in particular the 1989 loma prieta earthquake similar high intensities in the monterey bay area during both the 1989 and 1838 events indicate that the 1838 shock probably ruptured the loma prieta segment in addition to the peninsular segment of the san andreas fault if so the resulting earthquake would have been of moment magnitude m w 7 2 thus like segments of many other plate boundaries the loma prieta segment exhibits heterogeneous rupture in that sometimes it ruptures with the peninsular segment as in 1906 and probably in 1838 and at other times it ruptures alone as in 1989 in contrast the area of high intensities generated by the 1865 earthquake was centered in the santa clara valley and the eastern foothills of the santa cruz mountains indicating that the 1865 shock probably was located northeast of the loma prieta rupture and not on the san andreas fault in addition the felt areas taken to be one of the best measures of relative source size of modified mercalli intensities mmi v and vi for the 1865 shock are considerably smaller than that of the 1989 event relationships between felt areas of intensities v and vi and moment magnitude are developed for the san francisco bay area based on these relationships the average computed moment magnitudes for the 1865 1868 and 1890 earthquakes are 6 51 0 18 6 84 0 20 and 6 32 0 16 respectively if these results are correct then the loma prieta segment taken to include all faults within the san andreas fault zone i e within a zone up to a few kilometers wide appears to rupture with or without the peninsular segment every 76 11 years these data on repeat times may be the most accurate information now available for ascertaining the date of future rupture of that segment and for testing recurrence models the smaller size of the 1865 earthquake would be consistent with it being part of the long term seismic build up to the 1868 event rather than being paired with it as events of similar size if the 1865 earthquake did occur northeast of the loma prieta segment then a future source of that type located closer to san jose and the santa clara valley could pose a considerable hazard to the southern san francisco bay area on going searches of letters and diaries of missionaries and early settlers could yield new information that should help to further constrain the locations and magnitudes of these and other historic earthquakes

mountain glacier evolution in the iberian peninsula during the younger dryas abstract we review the evolution of glaciers in the iberian mountains during the younger dryas 12 9 11 7 ka following the chronology of greenland stadial 1 gs1 and compare with available environmental and climate data to investigate glacier dynamics during cold stadial episodes the best examples of younger dryas moraines are found in the central pyrenees involving short ice tongues up to 4 km in length in the highest massifs above 3000 m a s l of the southern versant small cirque glaciers and rock glaciers formed during the yd occurred in other pyrenean massifs in the cantabrian range and in the gredos and guadarrama sierras central range as indicated by several rocky polished thresholds that were ice free at the beginning of the holocene although some former rock glaciers were re activated during the younger dryas glacial activity was limited in the southernmost part of the iberian peninsula sierra nevada most iberian records show vegetation changes during the yd characterized by a forest decline and an expansion of shrubs mainly juniperus and steppe herbs although the vegetation response was not homogeneous because of variable resilience among ecosystems available records also document a variable lake response in terms of hydrology and productivity with a decrease in sedimentation rates and organic productivity in most high altitude lakes and increases in salinity and relatively lower lake levels at lower altitudes the impact of the younger dryas on the coastal environment was almost negligible but it was responsible for a brief cessation in sea level rise high resolution analyses of new speleothem records have documented a double structure for the yd with an earlier drier phase followed by a relatively more humid period the review of geomorphological evidence demonstrates a strong latitudinal control of glacial activity during the yd with more intense development in the northern than in the southern regions the increase in humidity during the second phase of the yd in southern latitudes could have been a decisive factor for glacier advance in the northern iberian mountains