the estimation of global sea level change a problem of uniqueness an objective method of estimating regional averages of coherent sea level sl change is developed the technique is applied to a large set of sl data representative of most of the world s continental margins the results show highly coherent sl changes over many of the regions studied the method is then applied to the regional averages themselves to develop an overall estimate of the coherent pattern of sl variations existing in the historical sl data set the pattern is characterized by a coherent rise of sl in all regions except alaska scandinavia both areas of notorious crustal uplift and southeast asia where sl appears to be falling the analysis suggests little or no change in sl prior to the early 1900 s the period since that time has seen an increase in sl that is optimally fit by a linear trend of 23 cm century the study results suggest that it is not possible to uniquely determine either a global rate of change of sl or even the average rate of change associated with the existing inadequate data set indeed different analysis methods by themselves can cause 50 variations in the estimates of sl trend in the existing data set a signal noise analysis suggests it should be easy to detect small future changes in the sl trends estimated for the period 1930 1980 however detection of theoretically predicted low frequency signals e g caused by co2 warming will be difficult in view of the huge low frequency natural variability associated with glacial tectonic processes

preliminary analysis of acceleration of sea level rise through the twentieth century using extended tide gauge data sets august 2014 this work explores the potential for extending tide gauge time series from the permanent service for mean sea level psmsl using historical documents psmsl ancillary data and by developing additional composite time series using near neighbor tide gauges the aim was to increase the number completeness and geographical extent of records covering most or all of the twentieth century the number of at least 75 complete century scale time series have been approximately doubled over the original psmsl data set in total over 4800 station years have been added with 294 of these added to 10 long southern hemisphere records individual century scale acceleration values derived from this new extended data set tend to converge on a value of 0 01 0 008 mm yr2 this result agrees closely with recent work and is statistically significant at the 1 sigma level possible causes of acceleration and errors are briefly discussed results confirm the importance of current data archeology projects involving digitization of the remaining archives of hard copy tide gauge data for sea level and climate studies

large inversions of altimeter and tied tide gauge data for the mediterranean sea mean surface satellite altimeter measurements and tide gauge data tied ttg data to a global geodetic reference frame by space techniques of positioning will provide in a near future consistent and complementary information to map the mean sea surface mss with a subdecimetric absolute accuracy information is consistent because after standard data processing both kinds of sea level measurements are given relative to the same geocentric reference ellipsoid information is also complementary because first satellite altimetry draws a dense sampling pattern of the ocean while ttg measurements are local second the properties of the data errors are very dissimilar in the two techniques both kind of sea level measurements are already available in the mediterranean basin this study is the first attempt to compute an accurate mss model with mixed sets of such data a total inverse method previously developed to analyze satellite altimetry is greatly improved in order to recover a full spectrum of the mss down to wavelengths 100 km and to invert rigorously large data sets including consecutive satellite tracks the mss solution derived solely from altimetry in the mediterranean sea has a formal error of 12 cm under the repeat satellite tracks up to 30 cm near the coasts with a further truncation error of 10 cm then an analysis of the discrepancy between this solution and ttg data allows us to point out unsuspected inconsistencies in the two data sets which are clearly identified nevertheless the usefulness of the ttg data is demonstrated by an estimate of their impact on the error spectrum of the mss

ocean signals in tide gauge records tide gauges are designed to measure changes in water level relative to land however vertical motions of the earth s crust manifest themselves as apparent water level changes in tide gauge records these crustally induced changes are often small in amplitude relative to the wide range of oceanic processes which affect water level in coastal regions vertical crustal motion can best be studied by first removing oceanic variability from the time series in this paper we summarize the major oceanic signals in tide gauge records we take the approach that the oceanic signals are unwanted noise in the data methods are described for removing or at least reducing the various oceanic signals these oceanic signals span a broad range of time scales from tides to interannual variability associated with the el nino phenomenon and secular sea level change from a number of oceanographic effects

time variations in the earth s gravity field detectable with geopotential research mission intersatellite tracking the geopotential research mission grm is a proposed system of two artificial satellites in tandem drag free polar orbits of low altitude 160 km designed for a detailed global mapping of the earth s gravitational and magnetic fields the mission should provide a large amount of new information about the gravity field particularly over continents resolving spatial variations in the gravity field as short as 100 km half wavelength however grm should also perform a much more difficult task the detection of time variations in the gravity field among the effects which produce changes in the field that are large enough to be detected by the intersatellite millimeter wavelength 1 s precision grm sensor are the following 1 rebound from ancient deglaciation 2 very large dip slip earthquakes 3 detailed ocean tides and 4 the seasonal growth and decline of continental glacial fields in particular many nonzonal as well as zonal components affected by postglacial rebound should be detected in a 6 month grm mission repeat passes over the fault zones of earthquakes similar to alaska 1964 chile 1960 or sumbawa 1977 should reveal signal changes due to their earth movements the effect of ocean tides on the grm signal should be readily detectable over a broad band of frequencies even if all but 10 of the tides are correctly modeled continued geophysical interest in these now largely unobserved phenomena warrants extension of the grm mission to somewhat higher altitudes

present and near future global sea level changes abstract values between 1 0 and 1 5 mm yr often quoted in the literature for the present day rate of eustatic sea level rise have been obtained in many cases by averaging records of tide gauge stations after having omitted areas of glacio isostatic or tectonic uplift though including areas of subsidence this approach results in an overestimation of the sea level rise which is increased by the fact that for geological reasons and human induced factors subsidence is expected to occur more frequently than uplift in oceanic and coastal areas in the absence of absolutely stable areas in the world a new approach is proposed which shows that on the atlantic coasts of europe when land movements are removed the sea level rise during the last century has been only 4 6 cm i e two to three times smaller than the estimation claimed by most authors this value is consitent with current computations of the recent effects on sea level of the thermal expansion of the ocean water 2 5 cm and of the melting of small glaciers 1 4 5 cm estimations of possible sea level changes during the next century diverge with different authors varying from a sea level drop of 7 cm to a sea level rise of over 3 5 m there are some problems however with the assumptions made and some feedback phenomena have not yet been taken into account in addition the relationship between the atmospheric co2 content temperature and sea level is far from being demonstrated for the recent past

morphological evolution of the guadiana estuary and intertidal zone in response to projected sea level rise and sediment supply scenarios analysis of holocene sediment accumulation in the guadiana estuary southern portugal during sea level rise since ca 13 cal ka bp was used to simulate the long term morphological evolution of the lower guadiana estuary and the associated intertidal zone for 21st century predicted sea level rises three sea level rise scenarios given by the ipcc 2007 were used in the simulations of morphology using a large scale behaviour oriented modelling approach sedimentation rate scenarios were derived both from the holocene evolution of the estuary and from a semi empirical estimation of present day sediment aggradation our results show that the net lateral expansion of the intertidal zone area would be about 3 5 of the present intertidal zone area for each 10 cm rise in sea level under constraints imposed by the lack of fluvial sediment supply the lateral expansion of the landward boundary of the intertidal zone will occur mainly in the portuguese margin of the guadiana estuary while submergence of the salt marshes will occur in the spanish margin therefore the spanish margin is highly vulnerable to both sea level rise and lack of sediment supply copyright 2011 john wiley sons ltd

new uranium series ages of the waimanalo limestone oahu hawaii implications for sea level during the last interglacial period abstract the waimanalo formation limestone of oahu has been correlated with the last interglacial period based on u series dating of corals by t l ku and colleagues the limestone consists of growth position corals and overlying coral conglomerate an apparent bimodal distribution of ages for the growth position corals mean age 133 ka and the overlying coral conglomerate mean age 119 ka has been interpreted to represent two distinct high stands of sea that occurred within the last interglacial period both growth position corals and overlying conglomerate coral occur in an outcrop east of kaena point and consist mainly of pocillopora and porites u series ages of growth position corals that show closed system conditions are 120 3 ka and 127 4 ka overlying conglomerate corals have u series ages that range from 120 3 ka to 138 4 ka at kahe point conglomerate corals have ages of 120 3 ka and 134 4 ka these data show that the growth position corals are not systematically older than the conglomerate corals thus there is no evidence for two distinct high stands of sea waimanalo deposits at kahe point and mokapu point new u series ages of 134 4 ka and 127 3 ka have beach deposits as high as 12 5 m and at mokapu point growth position corals as high as 8 5 m a last interglacial sea level stand of 8 5 to 12 5 m conflicts with estimates of 6 m from a number of tectonically stable coastlines and islands in the western atlantic ocean we infer therefore that oahu may be undergoing uplift at a low rate this uplift may be due to compensatory lithospheric flexure because the island of hawaii has been subsiding throughout much of the quaternary from volcanic loading because of this possible uplift oahu and islands like it elsewhere in the pacific cannot be used as reference points for sea level during the last interglacial period

combination of multisatellite altimetry and tide gauge data for determining vertical crustal movements along northern mediterranean coast sea level variations slv can be measured by tide gauges tg at the coast and by altimeters onboard satellites the former measures the slv relative to the coast whereas altimetry provides the slv with respect to a geocentric reference frame the differences between slv measurements from these two techniques can be used as an indirect assessment of vertical crustal motions at the tg sites in this study we exploit this idea analyzing differences between sea level signals as measured by altimetric missions topex poseidon and jason 1 and by 47 tg stations along northern mediterranean coasts for the period 1993 2007 this allows us to estimate the vertical land motion along these coasts at the tg sites in this time window for those sites where the tg is co located or has a nearby global positioning system gps station these estimates are compared with the vertical rates derived from gps measurements our results on vertical ground motion along the mediterranean coast provide a useful source of data for studying contrasting and constraining tectonic models for the region

variation of the mean sea level from topex poseidon data variations of the 10 day averaged sea level extracted from topex poseidon t p altimeter data are examined from october 1992 to february 1995 data are corrected from instrumental drifts and recent precise orbit and ocean tide corrections are used when data from the less accurate first eight cycles are excluded and atmospheric pressure effects are not corrected the 10 day mean sea level varies by 5 0 mm rms its variations can be described by a 4 1 1 mm yr drift a small annual signal of 2 7 mm amplitude and a residual signal of 3 5 mm rms amplitude and gaussian statistics close to formal error estimates the mean sea level rise is difficult to explain by drifts of geophysical corrections though the case for the wet tropospheric correction and that for the orbit are uncertain pressure effects should be corrected relative to the global pressure averaged over the ocean the latter shows a seasonal signal of 1 cm amplitude and apparent fluctuations of 30 to 70 day periods these fluctuations could result from errors in the atmospheric pressure fields but they seem to be mostly related to large regional pressure evolutions evidence is also found for a sampling effect by the t p orbit of pressure signals at shorter than 10 day periods pressure effects on sea level are then assumed to be an inverse barometer relative to 10 day global atmospheric pressure over the ocean which allows analysis of the geographical repartition of the mean sea level evolution due to other effects the mean sea level rise is comparable in the northern 4 2 2 5 mm yr and southern 3 7 1 9 mm yr hemispheres it seems mostly related to interannual variations of the tropical ocean 41 of the global signal and of the northern hemisphere subtropical gyres 30 of the global signal residual noise on these regional values seems inversely proportional to the square root of the number of data points in each area the hemispheric seasonal pressure variation relative to the globally averaged pressure over the ocean is less than 3 mm amplitude in our calculation it is implicitely assumed that it induces a small interhemispheric water mass exchange the amplitudes of the seasonal hemispheric sea level variations are 27 and 18 mm in the northern and southern hemispheres respectively these amplitudes are very close to being inversely proportional to the ocean surface in each hemisphere the maxima of sea level in these hemispheres are reached in the last weeks of september and march respectively at subpolar latitudes semiannual components are observed in each hemisphere which are consistent with those of sea surface temperature

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

relative sea level change from tide gauge records of western north america negligible success of investigators in relating tide gauge records of the west coast of north america to eustatic changes of sea level is the result of tectonic movements of the land reference level beneath the tide gauges the vertical tectonic movements are caused by horizontal movements of oceanic crustal plates sinking of 12 mm yr at cordova alaska is associated with intense subduction at the east end of the aleutian trench rising by 6 mm yr at skagway may be caused by resistance to lateral crustal movement toward the filled trench rising of 1 mm yr in southern alaska uplift above slow subduction little vertical movement between sitka and mendocino fracture zone translation and slow subduction including fracture zones and thick sediments sinking of 1 mm yr west of the san andreas fault translation and sinking of 2 mm yr along northwestern mexico effects of cooling of late rifted crust and only diagonal subduction superimposed on this tectonism due to plate motion is broad scale isostatic adjustment both rise and fall resulting from deglaciation removal of rigid plate motion deltas helps resolve subplate tectonic processes higher frequency 0 05 0 5 cpy sea level changes as well as large scale pressure fluctuations and wind stress events are associated with el nino southern oscillation an apparent increase in relative sea level rise near 1935 also observed in other regions remains to be explained

coastal neo tectonics of the mediterranean from tide gauge records abstract records from tide gauges in israel and egypt supplement the many geological and archeological investigations that have contributed information about relative sea level changes in the mediterranean region seven such records reveal changes during the past few decades that accord with prior inferences about land movements in this region emergence along the coast of israel and at alexandria and subsidence at the nile delta and the head of the gulf of suez twenty four other tide gauge records for the rest of the mediterranean region indicate more uniformity submergence of land or rise of sea level in the west but with greater movements of the land attributed to probable plate underthrusting in turkey and greece to volcanism near mount etna to deltaic compaction at izmir and to deltaic compaction coupled with water pumping at the po delta

mangrove bank sedimentation in a mesotidal environment with large sediment supply gulf of papua the most extensive mangrove forests on earth are associated with major river systems the indo pacific region has numerous large rivers that discharge onto broad continental shelves and mangroves occur widely along these coastlines in the gulf of papua gop alone there are 3350 km2 of mangrove forests the majority of which 2900 km2 are associated with the fly kikori and purari river deltas this study examines data from 28 vibracores to describe preserved sedimentary strata and to determine rates of sediment accumulation in this dynamic coastal environment the observations suggest a common stratigraphy is contained in prograding mangrove banks of the mesotidal western gop and that it is similar to mud dominated and physically stratified stratigraphy recorded by other intertidal areas with and without mangroves experiencing large tidal range 2 m and sediment supply e g ganges brahmaputra and yangtze river deltas grain size sedimentary structure radionuclide and remotely sensed data are analyzed and four stratigraphic facies are identified 1 supratidal to high tidal muds 2 mid tidal sandy muds 3 low tidal sand and mud and 4 subtidal channel sands supratidal and high tidal sediments of gop mangrove forests are typically muddy but can have high sand contents 30 in areas exposed regularly to ocean waves these muds can be homogenous but commonly have physical structures laminations and bedding probably reflecting high rates of sediment accumulation relative to bioturbation mangrove muds may have low water contents due to infrequent inundation and because of their cohesive nature and abundant roots can form steep intertidal banks and erosional scarps mid tidal and low tidal sediments are thinly laminated 2 mm laminations likely deposited from fluid mud transport channel sediments have thin and thick mud and sand laminations but are identified by thick 5 cm sand beds a conceptual model of mangrove bank progradation is created using sedimentological and radionuclide data maximum sediment accumulation rates were determined using steady state 210pb profiles and greatest mean rates are found in mid tidal areas 4 4 cm year 3 9 g cm2 year slower accumulation occurs in high tidal and low tidal areas 1 8 and 1 5 cm year respectively 1 2 and 1 0 g cm2 year respectively remotely sensed data indicate that areas of erosion and accretion co exist in the kikori purari region very large 210pb accumulation rates were measured in areas of significant accretion supporting the validity of the calculated rates in areas of rapid accretion cores can have non steady state or event related 210pb profiles reflecting episodic sedimentation or complex radionuclide scavenging dynamics most cores from the fly river delta are of this type sediment trapping in western gop mangroves is estimated to account for 2 14 of the total gop sediment load

influence of glacial isostatic adjustment on tide gauge measurements of secular sea level change modem tide gage records of secular sea level change are strongly contaminated by the ongoing influence of glacial isostatic adjustment in this paper we employ an accurate high resolution model of the glacial isostatic adjustment process to filter this signal from time series consisting of annual mean heights observed on over 500 tide gages from which records of duration longer than 10 years are available these records are all contained in the archive of the permanent service for mean sea level at bidston in the united kingdom prior to removal of the isostatic adjustment contamination from these records the secular sea level change signal is seen to exhibit both rising and falling levels depending upon geographic location with regions of falling level corresponding to those that were ice covered during the last glaciation event of the present ice age after filtering the geographic heterogeneity in rates is considerably reduced so much so that a globally coherent component consisting of a rise of sea level at a rate of 2 4 0 9 mm yr 1 is revealed this could conceivably be driven by the greenhouse effect although no particular mechanism has been unambiguously identified by our analyses we investigate the impact of a number of different variants of the analysis procedure upon the inferred global signal

late holocene changes in sea level and environment on eastern cape breton island nova scotia canada the late holocene history of a coastal basin in otter harbour on the great bras d or of cape breton island nova scotia was reconstructed using micro and macrofossils the pollen stratigraphy shows a decrease in oak and pine pollen percentages around 4000 bp while tsuga pollen reaches a maximum over the last 1000 years genera of the mixed hardwood forest have declined while boreal genera have increased suggesting climatic cooling in the region human influence from 400 bp to the present is evidenced by increased pteridophyte spores and pollen of rumex gramineae and ambrosia siliceous microfossils indicate that sea level in the great bras d or rose over the last 4000 years to 1 5 m below present level at 950 bp this rate of sea level rise 16 cm per century falls within the regional range of relative sea level rise in the maritimes of 10 30 cm per century for the last several thousand years however this long term rate in the maritimes is less than the rate of 30 35 cm per century determined from

trends of relative sea level change past present and future abstract past sea level trends are dominated by global tectonics geoid changes eustasy and global isostatic adjustments most of these factors have a global impact but at rates differing in time and place present sea level variations are measured by tide gauge recording oceanographic measurements and satellites determination of the present global eustatic sea level change remains a challenging problem however with the present weak eustatic factor being obscured by much stronger tectonic glacio isostatic oceanographic and atmospheric effects the co 2 content in the atmosphere has increased by about 30 since the start of world wide industrialization and it is expected that this rise will continue and perhaps accelerate over the next decades co 2 with other greenhouse gases are likely to increase the greenhouse effect which might lead to a rise in the temperature of the air and the ocean to a gradual melting of ice caps and to a global sea level rise to provide a sounder basis for the prediction of future sea level changes and their consequences a new interdisciplinary cooperation should deal with four interrelated topics 1 geologists and coastal geomorphologists determination of local trends of relative sea level change since the last interglacial maximum and during the late holocene this will provide a geological benchmark with which to assess the relative importance of projected anthropogenic changes 2 physical oceanographers and geodesists a constantly updated set of analyses of tide gauge data from the last two centuries to establish the existence of any acceleration in the current sea level trends 3 physical oceanographers climatologists and astronomers predictions of possible future sea level changes based on a critical review of existing models and on the development of new models on climate and on astronomical periodicities 4 geologists oceanographers coastal geomorphologists geographers environmentalists and engineers identification of the coastal areas throughout the world at greatest risk from changing sea levels and surge frequency and an assessment of potential environmental and infrastructural consequences

earthquakes and sea level space and terrestrial metrology on a changing planet the complacency with which man inhabits continent ocean margins or plate boundaries is based on the assumption that sea level rise and periodic seismicity are acceptable risks the forecast of future sea level or future seismicity is essential for informed assessment of these risks the historical data from which forecasts may be derived are in each case of limited antiquity and uneven spatial distribution developments in space geodesy and crustal deformation metrology in the past two decades offer the means to acquire a homogeneous global data set for monitoring relative vertical and horizontal motions of the earth s surface to within several millimeters these new tools are reviewed in terms of their application to forecasting trends in sea level rise and forecasting damaging earthquakes

martian xenon components in shergotty mineral separates locations sources and trapping mechanisms isotopic signatures and concentrations of xenon have been measured in shergotty mineral separates by laser step heating martian atmosphere and martian interior xenon are present as is a spallation component martian atmospheric xenon is 510 times more concentrated in opaque minerals magnetite ilmenite and pyrrhotite and maskelynite than in pyroxenes perhaps reflecting grain size variation this is shown to be consistent with shock incorporation a component consisting of solar xenon with a fission contribution similar to components previously identified in martian meteorites and associated with the martian interior is best defined in the pyroxene dominated separates this component exhibits a consistent 129xe 129xe 132xe 1 2 excess over solar planetary 129xe 132xe 1 04 we suggest that gas present in the melt perhaps a mixture of interior xenon and martian atmosphere was incorporated into the pyroxenes in shergotty as the minerals crystallized

coral indicators of past sea level change a global repository of u series dated benchmarks fossil corals provide valuable data for reconstructing past sea levels as they are often well preserved in the fossil record and can be dated with u series methods here we present a global and internally consistent database of usingle bondth dated fossil coral sea level indicators including full consideration of all known associated uncertainties both vertical and chronological we include carefully determined taxon specific depth distributions rather than blanket depth uncertainty terms as used in most previous work this is based on a synthesis of extensive modern ecological information on depth ranges these ranges are found to be spatially variable between ocean basins between regions and on sub regional scales because depth itself is not limiting instead depth distributions arise from complex physical chemical and biological interactions with coral reef growth distribution and composition one of the main causes for recognition of the greater depth variability of coral taxa has been the routine inclusion of deep diving and rov surveys in coral ecological studies over the past few decades which has broken through the shallow water bias of early surveys by adding frequent observations on deeper occurrences although more are needed it is also clear from our assessment that coral habitat depth distributions must be determined on the species level to reduce uncertainties in reconstructions of past sea levels and that application to sea level studies then requires these studies also to identify fossil corals to the species level samples identified only to the genus level give rise to wide uncertainties in habitat depth and hence sea level our database contains extensive metadata to assist evaluations of dating quality as well as geomorphic and stratigraphic metadata we demonstrate with examples how such metadata can help to evaluate sea level reconstructions for example by identifying outlier points one example discusses the last interglacial lig where we use the available data with their uncertainties to assess probabilistically the time at which local sea levels exceed that of the present which yields a mean age of 124 6 ka with 95 probability bounds at 118 5 and 129 5 ka we conclude with identification of key outstanding issues relating to i current incomplete understanding of tectonic setting including the current lack of independent verification of uplift subsidence rates and reliance of somewhat unsatisfactory and circular use of the elevation of last interglacial deposits ii the depth distributions of coral taxa and iii the complete documentation of stratigraphic geomorphological and other contextual information with suggestions for strategies to address these issues

the sequestration sink of soot black carbon in the northern european shelf sediments 1 to test the hypothesis that ocean margin sediments are a key final repository in the large scale biogeospheric cycling of soot black carbon soot bc an extensive survey was conducted along the 2 000 km stretch of the swedish continental shelf scs the soot bc content in the 120 spatially distributed scs sediments was 0 180 130 26 dw median with interquartile ranges corresponding to 5 of total organic carbon using side scan sonar constraints to estimate the areal fraction of postglacial clay sediments that are accumulation bottoms 15 of scs the soot bc inventory in the scs mixed surface sediment was estimated at 4 000 gg combining this with radiochronological constraints on sediment mass accumulation fluxes the soot bc sink on the scs was 300 gg yr which yielded an area extrapolated estimate for the northern european shelf nes of 1 100 gg yr this sediment soot bc sink is 50 times larger than the river discharge fluxes of soot bc to these coastal waters however of similar magnitude as estimates of atmospheric soot bc emission from the upwind european continent while large uncertainties remain regarding the large scale to global bc cycle this study combines with two previous investigations to suggest that continental shelf sediments are a major final repository of atmospheric soot bc future progress on the soot bc cycle and how it interacts with the full carbon cycle is likely to benefit from14c determinations of the sedimentary soot bc and similar extensive studies of coastal sediment in complementary regimes such as off heavily soot bc producing areas in s and e asia and on the large pan arctic shelf

australia an unstable platform for tide gauge measurements of changing sea levels a reply twenty five tide gauge records non uniformly distributed along the coast of australia were used to evaluate the stability of australia as a platform from which to measure changes in sea levels the spatial and temporal variabilities of relative sea levels were defined using a multivariate analytical tool eigenanalysis on 13 of these stations low frequency period 20 years and greater relative sea levels are believed to reflect the combined effects of subsistence due to sediment and water loading subsidence due to thermal cooling of oceanic crust and emergence along a convergent plate boundary global eustatic sea level rise cannot be identified unambiguously from these data but clearly it is not responsible for the observed patterns of relative sea level the straight average rate of rise of relative sea level around australia is 1 3 mm yr submergence with general submergence in the south at an average rate of 1 8 mm yr and emergence in the north 0 5 mm yr the latter an average of two sta