application of tephrochronology to the timing and correlation of palaeoceanographic events recorded in holocene and late glacial shelf sediments off north iceland abstract the north icelandic shelf is partly distinguished by the tjornes fracture zone featuring numerous active basins in a mud dominated shelf environment late glacial and holocene high resolution sedimentary records from this area have been studied with tephrochronology as the main tool for correlation and for exact timing of palaeoceanographic events in the area data from three new piston cores from the shelf demonstrate the importance of tephra markers for the first chronological evaluation and correlation of the cores the correlation is extended with lithological logs and with magnetic susceptibility records a detailed multidisciplinary study including biostratigraphy and tephrochronology of a late holocene record of predominantly muddy sediments at the same location demonstrates that marked variations in the distribution of water masses occurred repeatedly through the last 4500 cal yr of special interest is the exact timing of a marked drop in sea surface temperature in the area indicated by ice rafting debris concentration to about 50 years before the hekla 3 eruption which occurred at 2980 cal yr bp this appears to predate most records of a general cooling event in nw europe by a couple of centuries two different possible age models one based on 14c dates combined with tephra markers and one based on tephra markers alone are discussed in context with the problem of different marine reservoir ages of the water masses in the area

composition and origin of sediments on the mid oceanic kolbeinsey ridge north of iceland in order to characterize the sediments of the south kolbeinsey ridge and to determine the influence of morpho and hydrodynamic conditions in this area a comprehensive sedimentological investigation was combined with detailed geochemical analyses lithological composition and grain size are mainly controlled by the input from two different sources the submarine active mid ocean ridge and iceland coarse grained volcanic material dominates in the ridge area whereas fine grained detritus from iceland characterizes the adjacent basin further the distribution of these sediments is largely influenced by hydrodynamic conditions and redeposition processes strong bottom water currents indicated by the benthic foraminifer species cibicides lobatulus prevent extensive deposition of fine grained material on the top of the ridge the ridge slope is characterized by redeposited sediments of various grain sizes bulk sediment chemical analyses show element distribution patterns that are strongly correlated with the ratio of volcanic vs detritic particle composition this ratio reflects particle input and distribution processes two element associations are notable elements coupled with 1 ridge derived volcanic particles and 2 the detrital 2 m fraction which reflects weathered material from iceland

late holocene ca 4 ka marine and terrestrial environmental change in reykjarfjordur north iceland climate and or settlement core b997 328pc is from the landward side of a 100 m deep basin in reykjarfjordur a small fjord on the north coast of the northwest peninsula of iceland this is an area that can be severely affected by incursions of polar sea ice but has not suffered marked land erosion during the settlement period the core is 422 cm in length and consists principally of fine grained muds with in situ molluscs eleven ams 14c dates on molluscs indicate a constant sediment accumulation rate of ca 1 cm 10 yr 1 for the last 4280 50 yr bp we measured and derived a variety of proxies for indications of changes in the nearshore environment these included physical properties and grain size mass accumulation rates micropalaeontology pollen and foraminifera multivariate analysis and constrained clustering were used to define major changes in the proxies in several parameters the major change in the fjord environment occurred close to 1000 14c yr ago thus approximately coincident with the onset of the settlement of iceland other changes are noted at around 1600 and 3400 14c yr ago betula pollen disappears from the record ca 1500 yr bp and there are peaks in marine productivity occurring ca 2 and 3 4 ka a major decline in carbonate accumulation and a sharp increase in the cold water benthic foraminifer elphidium excavatum forma clavata 400 yr ago represents the local marine signature of the little ice age none of the changes in our data can be explained adequately by a simple call to land use practices and an increase in land to sea transport but both the pollen and foraminiferal records indicate a decrease and even loss of warm elements in both flora and fauna over the past 4 kyr copyright 2001 john wiley sons ltd

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

late holocene summer sea surface temperatures based on a diatom record from the north icelandic shelf diatom assemblages from a high resolution core on the north icelandic shelf reveal a general late holocene cooling trend which is interrupted by three relatively warm periods diatom data from sur

a calendar age estimate of the younger dryas holocene boundary at krakenes western norway the younger dryas holocene transition yd h in the sediments of krakenes lake western norway is well marked both lithologically and palaeobiologically at 756 5 cm in the investigated core a ser

late glacial and holocene palaeoceanography of the north icelandic shelf high resolution gravity cores and box cores from the north icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin iferal data results from two outer shelf cores covering the last 13 6 k 14 c yr bp are presented in this paper the sediments accumulated in north south trending basins on each side of the kolbeinsey ridge at water depths of ca 400 m sedimentation rates up to 1 5 m kyr 1 are observed during the late glacial and holocene the vedde and saksunarvatn tephras are present in the cores as well as the hekla 1104 a new tephra kol gs 2 has been identified and dated to 13 4 k 14 c yr bp and another tephra geochemically identical to the borrobol tephra has been found at the same level at present the oceanographic polar front is located on the north icelandic shelf which experiences sharp oceanographic surface boundaries between the cold east icelandic current and the warmer irminger current past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the polar front the area was deglaciated before ca 14 kyr bp but there is evidence of ice rafting up to the end of the gs 1 greenland stadial 1 younger dryas period increasing again towards the end of the holocene foraminiferal studies show a relatively strong gs 2 pre 13 kyr bp palaeo irminger current followed by severe cooling and then by unstable conditions during the remainder of the gi 1 greenland interstadial 1 bolling allerod and gs 1 younger dryas another cooling event occurred during the preboreal before the holocene current system was established at about 9 kyr bp after a climatic optimum between 9 and 6 kyr bp the climate began to deteriorate and fluctuate copyright 2000 john wiley sons ltd

a record of pliocene and pleistocene glaciations and climatic changes in the north atlantic based on variations in volcanic and sedimentary facies in iceland abstract the location of iceland directly below the arctic circle and on the north atlantic plate boundary gives the island a characteristic record of interbedded lavas glacial deposits and other sediments opening a window on the geological and climatic history of the north atlantic frequently extruded lava flows tend to shield underlying sediments from subsequent erosion explosive volcanism keeps the sedimentation rate high and produces extensive time markers continuing studies of diamictites interbedded within basaltic lava suites of cainozoic age in iceland deal specifically with the problem of differentiating between glacial and non glacial sediments that have very similar attributes a multifaceted approach has been taken in order to differentiate these deposits this includes both lateral and vertical lithofacies description and clast fabric studies based on extensive field work a comparison with modern analogues and detailed laboratory work textural studies on thin sections and palaeomagnetic studies the results suggest that both the nature and extent of late pliocene and early pleistocene glaciations can be inferred from the preserved record the rock sequence offers excellent opportunities for pinning down the age of each event through palaeomagnetic correlation and radiometric dating of the lava flows the oldest tillite along the north coast of iceland has been bracketed down to approximately 2 1 ma and in inland mid western iceland to approximately 2 6 ma it is anticipated that continuing work elsewhere in iceland can further define the trends of pliocene glaciation in the north atlantic the significance of the frequency of identified glacial deposits in the icelandic sections may be tested through comparison with the latest deep sea record of glacial interglacial cycles

ice induced vertical circulation in an arctic fiord ctd and nutrient data taken in south cape fiord next to a glacier face show strong evidence of upwelling in addition a region of down welling is found from 0 5 km to 5 km from the ice intruding layers with thicknesses consistent with lab measurements are found near the ice a phytoplankton bloom is found to be going on in the fiord and an upwelling velocity of 2 5 10 4 m s 1 is calculated by assuming that all the nitrogen required by these cells is up welled from the deep water within 10 2 m of the glacier mechanisms to drive the downwelling are discussed

a 9000 year old ash bed on the faroe islands abstract radiocarbon datings of the saksunarvatn ash bed on the faroe islands indicate an age of 9000 9100 yr b p the saksunarvatn ash bed differs geochemically from both ash zone 1 in the north atlantic and the vedde ash bed of norway and the norwegian sea all mentioned ashes are assumed to originate from iceland the vedde ash has been dated at 10 600 60 yr b p consequently the saksunarvatn and vedde ash beds provide an opportunity for precise dating of events around the pleistocene holocene boundary in marine cores especially from the region where the two plumes overlap

late weichselian marine 14c reservoir ages at the western coast of norway abstract a shallow marine late weichselian deposit on the outer coast of western norway contains both terrestrial plant material and articulated marine shells we have 14 c dated both types of material from eight different stratigraphic levels covering the time interval 12 300 to 11 100 14 c yr b p the difference between 14 c dated terrestrial plant material and marine shell material the marine reservoir age ranges from 200 to 525 yr with a weighted average of 380 32 yr this is almost identical to the present reservoir age of 379 20 yr for southern norway in the mid younger dryas yd interval the reservoir age in the north atlantic 55 n 65 n was 700 800 yr considerably greater than the present reservoir age and the age we have measured for the bolling allerod interval the reason for this increase during the yd is probably a combination of reduced inflow of surface waters to the north atlantic and more extensive sea ice cover evidence from marine cores show that the southeastern norwegian sea experienced rapid fluctuations in the inflow of warm atlantic surface water during the period 12 300 to 11 000 yr b p however the reservoir age apparently did not increase during these colder periods older dryas i and ii the reason is probably that in contrast to the yd these colder periods did not last long enough and or were of too limited extent to alter the reservoir age of the ocean a comparison of the obtained 14 c dates with the varve 14 c chronology from lake suigetsu indicates an age of 12 770 cal yr b p for the al yd boundary

biostratigraphic evidence of the allerod younger dryas preboreal oscillation in northern iceland basal sediments of lake torfadalsvatn northern iceland record changes in terrestrial and limnic environments in the period 11 300 9000 14c yr b p these changes were probably forced by climate and connected with displacements of the marine polar front and sea ice margin pollen spores green algae pediastrum saturation isothermal remanent magnetization and carbon content of the basal sediments provide the first detailed biostratigraphic record of the last glacial interglacial transition in iceland during the first pioneer phase beginning at ca 11 300 14c yr b p grasses and fell field herbs became established and lake productivity was very low at ca 10 900 14c yr b p climatic and soil conditions became favorable for shrubs and dwarf shrubs this change together with increased limnic productivity clearly indicates long seasons without ice cover in the sea immediately north of iceland a return to a colder climate younger dryas probably in connection with a southward displacement of the marine polar front occurred by 10 600 14c yr b p shrub and dwarf shrub vegetation disappeared and limnic productivity diminished a second pioneer vegetation phase dominated by oxyria rumex and grasses was initiated by a change to longer seasons without sea ice at ca 9900 14c yr b p this warming is also evident as a contemporaneous increase in lake productivity after ca 9400 14c yr b p the reestablishment of dwarf shrub heaths and very high limnic productivity indicate further warming

depositional regimes in the norwegian greenland sea the last two glacial to interglacial transitions various models of surface and deep water circulation in the norwegian greenland sea ngs have been proposed for the last two glacial to interglacial transitions although much progress has been made in understanding the sedimentary response to climatic and oceanographic changes conflicting interpretations have been developed to clarify some of these discrepancies and to test or modify the existing circulation concepts a multiparameter approach is applied combining sedimentological micropaleontological organic geochemical and isotopic methods on the basis of indicative properties a combined litho and organofacies concept is developed and calibrated with modern depositional settings beneath different surface water masses sedimentary regimes are then derived for glacial and deglacial settings

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

a metric for surface heat flux effect on horizontal sea surface temperature gradients understanding what controls horizontal variations in sea surface temperatures ssts is one of the key science questions in climate research although various oceanic effects contribute to reinforcement relaxation of horizontal variations in ssts the role of surface heat fluxes is surprisingly complex and can lead to significant biases in coupled models if improperly represented in particular the contribution of surface heat fluxes to surface frontogenesis frontolysis depends not just on their gradients but also on the distribution of mixed layer depth which controls the effective heat capacity of the upper ocean in this study a new metric referred to as the surface flux frontogenesis metric is proposed that quantifies the relative importance of horizontal variations in surface heat fluxes and mixed layer depth global maps of this metric reveal that the role of surface heat fluxes in determining the horizontal sst gradient is highly variable geographically and by season furthermore the metric can help explain characteristics of sst fronts in the northwestern pacific the southern ocean the eastern equatorial pacific and the west coast of north america implications of this metric in coupled models will also be discussed

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

environmental change in eastern greenland during the last 1300 years evidence from foraminifera and lithofacies in nansen fjord 68 n lithofacies and benthic foraminiferal analyses of two sediment cores bs1191 k13b and k14 from nansen fjord eastern greenland show evidence of changing oceanographic and sea ice conditions from

magma emission rates from shallow submarine eruptions using airborne thermal imaging abstract the effusion rate is the most important parameter to gather when a volcanic eruption occurs because it controls the way in which a lava body grows extends and expands influencing its dimensional properties calculation of lava flow volume from thermal images collected by helicopter surveys has been largely used during the last decade for monitoring subaerial effusive eruptions however due to the depths where volcanic activity occurs monitoring submarine volcanic eruptions is a very difficult task the 2011 2012 submarine volcanic eruption at el hierro canary islands has provided a unique and excellent opportunity to monitor eruptive processes occurring on the seabed the use of a hand held thermal camera during daily helicopter flights allowed us to estimate for the first time the daily and total erupted magma volumes from a submarine eruption the volume of magma emitted during this eruption has been estimated at 300 mm3 giving an average effusion rate of 25 m3 s 1 thermal imagery by helicopter proved to be a fast inexpensive safe and reliable technique of monitoring volcanic eruptions when they occur on the shallow seabed

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

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

chronology of late holocene climatic events in the northern north atlantic based on ams 14c dates and tephra markers from the volcano hekla iceland a combination of ams14c dating and tephrochronology has been used to date late holocene oceanographic events in a 335 cm marine record covering about 4600 cal yr with sedimentation rates exceeding 80 cm 1000 yr 1 the core site is located 50 km offshore on the northern icelandic shelf tephra markers from iceland serve to correlate the marine and terrestrial records especially notable is the presence of three geochemically correlated tephra markers from the icelandic volcano hekla hekla 4 hekla 3 and hekla 1104 benthic and planktonic foraminiferal abundance and distribution as well as the petrography of the sand fraction of the muddy shelf sediments are used as palaeoceanographic proxies the foraminiferal assemblages reflect a general cooling trend during the last 4600 yr a marked drop in sea surface temperatures is registered at about 3000 cal yr bp corresponding to the level of the hekla 3 tephra there is faunal indication of temperature amelioration during the medieval warm period and a cooling again during the little ice age periods of ice rafting events are indicated by ice rafted debris ird concentrations e g at around 3000 cal yr bp and during the little ice age the former event occurred just prior to the deposition of the hekla 3 tephra marker the largest holocene hekla eruption a correlation with terrestrial climatic events in iceland is presented a standard marine reservoir correction of 400 14c yr appears to be reasonable at least during periods with high influence of water masses from the irminger current on the northern icelandic shelf an increase to ca 530 14c yr may have occurred however when water masses derived from the east greenland current were dominant in the area copyright 2000 john wiley sons ltd

holocene palaeoclimatic reconstruction in northern iceland approaches and results abstract the period since the mid 19th century when instrumental meteorological recording first started in iceland has shown climate conditions close to or even at both holocene minimum and optimum levels the 19th century part of the little ice age represents a thermal minimum whilst the warmest decades of the 20th century are close to the estimated holocene thermal maximum a model describing sea ice climate ela relationships in northern iceland for this period has been developed providing a calibrated proxy climate record as a basis for palaeoclimatic reconstruction for the holocene as a whole glacier advances in the periods around 4700 bp around 4200 bp ca 3200 3000 bp around 2000 bp around 1500 bp and around 1000 bp based on radiocarbon dating and tephrochronology mark climatic minima of the post preboreal holocene when conditions were comparable to the extremes in the second half of the 19th century compared to optimal holocene thermal conditions with temperatures at least as high as in the 1930s the range of holocene temperature variation was ca 3 k this was accompanied by a doubling in precipitation from the thermal minima to the maxima

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

achieving high resolution thermal imagery in low contrast lake surface waters by aerial remote sensing and image registration abstract a two platform measurement system for realizing airborne thermography of the lake surface water temperature lswt with 0 8 m pixel resolution sub pixel satellite scale is presented it consists of a tethered balloon launched imaging and monitoring platform blimp that records lswt images and an autonomously operating catamaran called zivicat that measures in situ surface near surface temperatures within the image area thus permitting simultaneous ground truthing of the blimp data the blimp was equipped with an uncooled infrared ir camera the zivicat was designed to measure along predefined trajectories on a lake since lswt spatial variability in each image is expected to be low a poor estimation of the common spatial and temporal noise of the ir camera nonuniformity and shutter based drift respectively leads to errors in the thermal maps obtained nonuniformity was corrected by applying a pixelwise two point linear correction method based on laboratory experiments a probability density function pdf matching in regions of overlap between sequential images was used for the drift correction a feature matching based algorithm combining blob and region detectors was implemented to create composite thermal images and a mean value of the overlapped images at each location was considered as a representative value of that pixel in the final map the results indicate that a high overlapping field of view 95 is essential for image fusion and noise reduction over such low contrast scenes the in situ temperatures measured by the zivicat were then used for the radiometric calibration this resulted in the generation of lswt maps at sub pixel satellite scale resolution that revealed spatial lswt variability organized in narrow streaks hundreds of meters long and coherent patches of different size with unprecedented detail

thermohaline steps induced by melting of the erebus glacier tongue a vertically stable step like thermohaline structure is observed throughout a continuous 400 m conductivity temperature depth ctd profile taken near the erebus glacier tongue mcmurdo sound antarctica the pattern is best developed between the sea surface and 250 m depth the interval corresponding to that of the irregular underwater profile of the glacier tongue the steps average 17 m in thickness and typically display discontinuities of 0 1 c in temperature 0 04 in salinity and 3 5 10 4 g cm 3 in density the observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water at this location subsurface seawater is inferred to remain above the in situ freezing point year round and contains sufficient heat to account for much of the glacier tongue thinning by basal melting an adequate volume of meltwater would result to produce the measured salinity steps we discuss related observations and some implications of this process for ocean circulation and biological productivity in the antarctic

coupled changes in sand grain size and sand transport driven by changes in the upstream supply of sand in the colorado river relative importance of changes in bed sand grain size and bed sand area sand transport in the colorado river in marble and grand canyons was naturally limited by the upstream supply of sand prior to the 1963 closure of glen canyon dam the river exhibited the following four effects of sand supply limitation 1 hysteresis in sediment concentration 2 hysteresis in sediment grain size coupled to the hysteresis in sediment concentration 3 production of inversely graded flood deposits and 4 development or modification of a lag between the time of a flood peak and the time of either maximum or minimum depending on reach geometry bed elevation construction and operation of the dam has enhanced the degree to which the first two of these four effects are evident and has not affected the degree to which the last two effects of sand supply limitation are evident in the colorado river in marble and grand canyons the first three of the effects involve coupled changes in suspended sand concentration and grain size that are controlled by changes in the upstream supply of sand during tributary floods sand on the bed of the colorado river fines this causes the suspended sand to fine and the suspended sand concentration to increase even when the discharge of water remains constant subsequently the bed is winnowed of finer sand the suspended sand coarsens and the suspended sand concentration decreases independently of discharge also associated with these changes in sand supply are changes in the fraction of the bed that is covered by sand thus suspended sand concentration in the colorado river is likely regulated by both changes in the bed sand grain size and changes in the bed sand area a physically based flow and suspended sediment transport model is developed tested and applied to data from the colorado river to evaluate the relative importance of changes in the bed sand grain size and changes in the bed sand area in regulating suspended sand concentration although the model was developed using approximations for steady uniform flow and other simplifications that are not met in the colorado river the results nevertheless support the idea that changes in bed sand grain size are much more important than changes in bed sand area in regulating the concentration of suspended sand published by elsevier b v