Rate Of Sea-level Change Research Articles

Inter-annual and decadal sea level variations in the north-western Pacific marginal seas

Long term sea level changes in the Okhotsk, Japan/East, East China and Yellow Seas have been explored based on mean monthly values of sea level from tide gauge and altimetry measurements. The analysis of low frequency sea level variability reveals clearly differentiated areas: the Okhotsk Sea and the northern sector of the Japan/East Sea display lower sea level variances and no sea level rise. The southern Japan/East Sea presents larger sea level variability associated with the circulation regime of the warm current entering through the Tsushima Strait and inter-annual sea level variations that are driven by steric and atmospheric changes. The largest sea level variances are found in the Yellow Sea due to the effect of atmospheric forcing over the continental shelf. Inter-annual variability is spatially varying within the Yellow Sea and the East China Sea and is mainly related to the steric sea level changes. Regional mean sea level indices have been synthesized for each area using the longest tide gauge records and have revealed correlations between the southern Japan/East and Yellow Seas with PDO and NP climatic indices. Linear trends at coastal sites in the Japan/East, East China and Yellow Seas show a rather heterogeneous pattern, with values between −1.5 and 5.5mm/yr for the period 1960–2000. During the period 1993–2008 linear trends derived from coastal tide gauges and from altimetry observations are coherent and reveal a southwards increasing pattern with maximum averaged values reached at the Yellow Sea (4.9±1.9mm/yr) followed by the Japan/East Sea (3.8±0.9mm/yr). Decadal rates of sea level change show distinct behaviour among basins as well as with the global average. The southern Japan/East Sea, the East China Sea and the Yellow Sea display decadal variability which is out of phase with respect to the global values.

Refining the model of barrier island formation along a paraglacial coast in the Gulf of Maine

Details of the internal architecture and local geochronology of Plum Island, the longest barrier in the Gulf of Maine, have refined our understanding of barrier island formation in paraglacial settings. Ground-penetrating radar and shallow-seismic profiles coupled with sediment cores and radiocarbon dates provide an 8000-year evolutionary history of this barrier system in response to changes in sediment sources and supply rates as well as variability in the rate of sea-level change. The barrier sequence overlies tills of Wisconsinan and Illinoian glaciations as well as late Pleistocene glaciomarine clay deposited during the post-glacial sea-level highstand at approximately 17ka. Holocene sediment began accumulating at the site of Plum Island at 7–8ka, in the form of coarse fluvial channel-lag deposits related to the 50-m wide erosional channel of the Parker River that carved into underlying glaciomarine deposits during a lower stand of sea level. Plum Island had first developed in its modern location by ca. 3.6ka through onshore migration and vertical accretion of reworked regressive and lowstand deposits. The prevalence of southerly, seaward-dipping layers indicates that greater than 60% of the barrier lithosome developed in its modern location through southerly spit progradation, consistent with a dominantly longshore transport system driven by northeast storms. Thinner sequences of northerly, landward-dipping clinoforms represent the northern recurve of the prograding spit. A 5–6-m-thick inlet-fill sequence was identified overlying the lower stand fluvial deposit; its stratigraphy captures events of channel migration, ebb-delta breaching, onshore bar migration, channel shoaling and inlet infilling associated with the migration and eventual closure of the inlet. This inlet had a maximum cross-sectional area of 2800m2 and was active around 3.5–3.6ka. Discovery of this inlet suggests that the tidal prism was once larger than at present. Bay infilling, driven by the import of sediment into the backbarrier environment through tidal inlets, as well as minor sediment contribution from local rivers, led to a vast reduction in the bay tidal prism. This study demonstrates that, prior to about 3ka, Plum Island and its associated marshes, tidal flats, and inlets were in a paraglacial environment; that is, their main source of sediment was derived from the erosion and reworking of glaciogenic deposits. Since that time, Plum Island has been in a state of dynamic equilibrium with its non-glacial sediment sources and therefore can be largely considered to be in a stable, “post-paraglacial” state. This study is furthermore the first in the Gulf of Maine to show that spit accretion and inlet processes were the dominant mechanisms in barrier-island formation and thus serves as a foundation for future investigations of barrier development in response to backbarrier infilling.

Evolution of a coupled marine ice sheet–sea level model

We investigate the stability of marine ice sheets by coupling a gravitationally self‐consistent sea level model valid for a self‐gravitating, viscoelastically deforming Earth to a 1‐D marine ice sheet‐shelf model. The evolution of the coupled model is explored for a suite of simulations in which we vary the bed slope and the forcing that initiates retreat. We find that the sea level fall at the grounding line associated with a retreating ice sheet acts to slow the retreat; in simulations with shallow reversed bed slopes and/or small external forcing, the drop in sea level can be sufficient to halt the retreat. The rate of sea level change at the grounding line has an elastic component due to ongoing changes in ice sheet geometry, and a viscous component due to past ice and ocean load changes. When the ice sheet model is forced from steady state, on short timescales (<∼500 years), viscous effects may be ignored and grounding‐line migration at a given time will depend on the local bedrock topography and on contemporaneous sea level changes driven by ongoing ice sheet mass flux. On longer timescales, an accurate assessment of the present stability of a marine ice sheet requires knowledge of its past evolution.

Intensifying Pacific trade winds drive regional sea level trends

Sea level in the western tropical Pacific Ocean has been increasing at a rate about 3 times the global average rate of sea level rise, as observed from satellite altimetry and tide gauges. Why are sea level trends so much different in this region? Previous studies have suggested that the high rate of sea level change in the western tropical Pacific is associated with the natural variation of the El Niño–Southern Oscillation. However, using a general circulation model, Merrifield and Maltrud show that western tropical Pacific sea level trends are likely due to a gradual intensification of the Pacific trade winds in the past 2 decades. They also highlight other aspects of ocean circulation that have been altered in response to the intensifying trade winds. Some previous research has suggested that the trade wind intensification is a result of global warming, although that has yet to be verified. If that is the case, the authors conclude, the western tropical Pacific sea level trends will likely continue to be anomalously high. (Geophysical Research Letters, doi:10.1029/2011GL049576, 2011)

Coastal sea level rise in southern Europe and the nonclimate contribution of vertical land motion

In this study, we extend the advanced approach of combining tide gauge and satellite altimetry data with supplemental equations from adjacent tide gauge records of at least 30 years of common data to investigate the relative importance of the nonclimate contribution of vertical land movement to the observed rates of sea level change along the coasts of southern Europe. The sensitivity tests proved that the advanced approach is robust and accurate at the submillimeter per year level of around 0.4 mm yr−1in estimating rates of vertical land movements. It enabled identifying stations displaying large rates of vertical land movements that must be taken into account when predicting future sea level rise and appraising the exposure to its impacts on populations and assets. The average rate of coastal climate‐related sea level rise in the Mediterranean Sea was consequently revisited to be of 1.7 mm yr−1 over the past century, whereas the Atlantic northern Iberian coast revealed a significant high rate of sea level rise in excess of 3.4 mm yr−1 for the past 70 years. Future work should consider applying this powerful approach to other geographic contexts as a useful source of supplementary data for geodynamic studies.

Systems tract successions under variable climatic and tectonic regimes: A quantitative approach

Systems tracts are linkages of contemporaneous depositional systems that accumulate under specific conditions of accommodation and sediment supply. They are identified by their stratal stacking pattern and position within the sequence. In practice, it is often difficult to assign accurately relative sea-level position to stacking patterns. Observations also show that systems tracts may succeed each other in different orders, not necessarily according to the prediction of an ideal model. The purpose of this study is to analyze the quantitative conditions for different possible combinations of systems tractswithin a cycle of relative sea-level change. Icehouse and greenhouse eustatic trends, active and passive tectonics, and varying depositional rates are considered as conditions. The systems tracts were defined based on the rate of accommodation change and depositional rate.Our quantitative calculations revealed that if the tectonics is active and the basement motion-time curve is segmented with sharp turning points between segments, eight possible successions of systems tracts may occur. If the basement motion is transitional between segments of subsidence and uplift, six scenarios are possible. Only three possible combinations of systems tracts can form in a sea-level cycle if the basement tectonics is passive. Variable depositional rate alone can be responsible for four different combinations of systems tracts under similar accommodation conditions. These combinations of systems tracts may occur primarily in greenhouse world. Eustasy under icehouse climatic conditions has rapid rates of change (up to 4000 m/myr), which are likelymany times faster thanwhat subsidence/uplift rates realistically can reach.As a consequence, only the full series of systems tract in the order of forced regression-lowstand normal regression-transgression-highstand normal regression can be predicted in icehouse, although the thickness of systems tracts in the real rock record may be rather small because of the fast rate of sea-level change.

Correction to “Long‐term and recent changes in sea level in the Falkland Islands”

In the paper “Long-term and recent changes in sea level in the Falkland Islands” by P. L. Woodworth et al. (Journal of Geophysical Research, 115, C09025, doi:10.1029/2010JC006113, 2010), in paragraph 47 we adopted a value of −0.52 mm/yr for the estimated rate of present-day sea level change in the Falkland Islands due to glacial isostatic adjustment (GIA). This value was used to remove the contributions of GIA to our measurements of historical and recent rates of sea level change. However, it was based on a misreading of the data file of Peltier [2004] on the Permanent Service for Mean Sea Level Web site (http://www.psmsl.org/train_and_info/geo_signals/gia/peltier). More reasonable values to apply to the observed changes since the mid-nineteenth century and in recent years would be −0.69 and −0.61 mm/yr respectively. Consequently, the long-term rate of sea level change between 1842 and the early 1980s, after correction for air pressure effects and for GIA, reported as +0.75 ± 0.35 mm/yr in paragraphs 1, 47, 55, and 61 should be +0.92 ± 0.35 mm/yr, the corresponding rate between 1842 and the midpoint of recent data of 1.06 ± 0.22 mm/yr in paragraphs 48 and 55 should be 1.23 ± 0.22 mm/yr, and the corresponding rate since 1992 reported as 2.51 ± 0.58 mm/yr in paragraphs 1 and 52 becomes 2.60 ± 0.58 mm/yr. The middle of paragraph 63 becomes “The Stanley data suggest that the rate of change of sea level in East Falkland since 1992 has been approximately 2.6 mm/yr, a rate supported by information from satellite altimetry.” These small GIA model corrections have no bearing on the main findings of our paper on the difference in the rates of sea level change between the historical (1842 to present-day) and recent (last 2 decades) epochs

Sea level variations at tropical Pacific islands since 1950

The western tropical Pacific is usually considered as one of the most vulnerable regions of the world under present-day and future global warming. It is often reported that some islands of the region already suffer significant sea level rise. To clarify the latter concern, in the present study we estimate sea level rise and variability since 1950 in the western tropical Pacific region (20°S–15°N; 120°E–135°W). We estimate the total rate of sea level change at selected individual islands, as a result of climate variability and change, plus vertical ground motion where available. For that purpose, we reconstruct a global sea level field from 1950 to 2009, combining long (over 1950–2009) good quality tide gauge records with 50-year-long (1958–2007) gridded sea surface heights from the Ocean General Circulation Model DRAKKAR. The results confirm that El Niño-Southern Oscillation (ENSO) events have a strong modulating effect on the interannual sea level variability of the western tropical Pacific, with lower/higher-than-average sea level during El Niño/La Niña events, of the order of ± 20–30 cm. Besides this sub-decadal ENSO signature, sea level of the studied region also shows low-frequency (multi decadal) variability which superimposes to, thus in some areas amplifies current global mean sea level rise due to ocean warming and land ice loss. We use GPS precise positioning records whenever possible to estimate the vertical ground motion component that is locally superimposed to the climate-related sea level components. Superposition of global mean sea level rise, low-frequency regional variability and vertical ground motion shows that some islands of the region suffered significant ‘total’ sea level rise (i.e., that felt by the population) during the past 60 years. This is especially the case for the Funafuti Island (Tuvalu) where the “total” rate of rise is found to be about 3 times larger than the global mean sea level rise over 1950–2009.

A 100 yr record of ocean temperature control on the stability of Jakobshavn Isbrae, West Greenland

An understanding of the interaction between ice sheet dynamics and forcing mechanisms, such as oceanic and atmospheric circulation, is important because of the potential contribution of these processes to constraining models that seek to predict future rates of sea-level change. Here we report new benthic foraminiferal data from Disko Bugt, West Greenland, showing a close correlation between subsurface ocean temperature changes and the ice margin position of the glacier Jakobshavn Isbrae over the past 100 yr. In particular, our faunal data show that warm ocean currents entered a bay, Disko Bugt, during the retreat phases of Jakobshavn Isbrae from A.D. 1920 to 1950 and since 1998. We also show a link between West Greenland ocean temperature and the Atlantic Multidecadal Oscillation, a key climate indicator in the North Atlantic Ocean. The close coupling between the oceans and the cryosphere identified here should be assessed in future projections of sea-level change.

A long-term trend and temporal fluctuations of the sea level at the Polish Baltic coast

Abstract The analysis of sea level record series along the Polish coast is presented. The main aim was to identify linear trends in the sea level changes at the coastal (Świnoujście, Kołobrzeg, Ustka, Łeba, Władysławowo, Hel, Gdynia, Gdańsk), lagoonal (Trzebież, Tokmicko) and riverine (Szczecin) gauge stations. The analysis showed individual coastal stations to differ in the rate of sea level changes. During 60 years of continuous observations (1947–2006), the differences varied from 1.0 (the western part of the coast) to 2.5 mm year−1 (the eastern part of the coast). The longest, more than 100-yr-long data series showed the sea level rise in Świnoujście and Kołobrzeg to be about 0.5 mm year−1; 1.57 mm year−1 being revealed in Gdańsk. Spectral analysis applied to the data showed numerous fluctuations and cyclicity in changes of the annual mean sea level at the Polish coast. A distinct, major 3-year cycle was revealed. In addition, three secondary cycles of 4.6, 6.7, and 8.6 years were present in the data, more or less clearly identifiable at individual stations.

Nineteenth and Twentieth Century Changes in Sea Level

Following the Last Glacial Maximum (25,000–20,000 years ago), sea level rose at rates on the order of several tens of millimeters per year at times, and increased overall by over 130 m. However, melting of the great ice sheets was largely complete by 6,000 years ago, and it is believed that sea level did not rise significantly again until recently. The rates of sea level change during the last few centuries and in recent decades can be measured in units of millimeters per year and are particularly important in understanding present-day climate change. We now have a range of techniques with which sea level changes can be measured and thus studied more intensively than before, as a global average and in each region. This article introduces each of the main data sets and presents the primary research findings. It is hoped that a greater understanding of the reasons for past observed sea level change, discussed elsewhere in this issue, will lead to better estimation of the changes likely to occur in the future

Geodetic observation of sea-level change and crustal deformation in the Baltic Sea region

Based on tide gauge observations spanning almost 200 years, homogeneous time series of the mean relative sea level were derived for nine sites at the southern coast of the Baltic Sea. Our regionally concentrated data were complemented by long-term relative sea-level records retrieved from the data base of the Permanent Service for Mean Sea Level (PSMSL). From these records relative sea-level change rates were derived at 51 tide gauge stations for the period between 1908 and 2007. A minimum observation time of 60 years is required for the determination of reliable sea-level rates. At present, no anthropogenic acceleration in sea-level rise is detected in the tide gauge observations in the southern Baltic. The spatial variation of the relative sea-level rates reflects the fingerprint of GIA-induced crustal uplift. Time series of extreme sea levels were also inferred from the tide gauge records. They were complemented by water level information from historic storm surge marks preserved along the German Baltic coast. Based on this combined dataset the incidence and spatial variation of extreme sea levels induced by storm surges were analysed yielding important information for hazard assessments. Permanent GPS observations were used to determine recent crustal deformation rates for 44 stations in the Baltic Sea region. The GPS derived height change rates were applied to reduce the relative sea-level changes observed by tide gauges yielding an estimate for the eustatic sea-level change. For 13 tide gauge-GPS colocation sites a mean eustatic sea-level trend of 1.3mm/a was derived for the last 100 years.

Holocene submerged shorelines on Theologos area (Greece)

Summary. Detailed mapping of coastline around Theologos area revealed the existence ofwell developed permanently submerged notches 75 10 cm below present mean sea level. Theregional occurrence of well preserved submerged tidal notches suggests their coseismic origin.The submergence of this Holocene shoreline possibly occurred at 1894 AD. Average submer-gence rate of 6.08 mm/yr may be estimated by a well preserved recumbent U-shaped notch.The retreating point depth suggests that the developing period of the notch might have beenof the order of as much as three thousand years.Several non in situ large rock blocks, containing marine fossils ( Lithophaga , Vermetids , Serpulids ) in growth position, seem to have been projected on the coast by a tsunami wave,which might have been caused by the same coseismic episode. Key words: notches, Sea-level changes, earthquake, tsunami, submergence rate 1 Introduction Tidal notches that usually undercut limestone cliffs in the mid-littoral zone are wellknown as precise sea-level indicators ( Pirazzoli 1986, 1996, 2005). In areas shelteredfrom wave action, elevated or submerged notches can be used to indicate former sea-level positions, with up to a decimeter confidence. The shape of the notch profilesmay also provide qualitative information on the rate of sea-level change and on tec-tonic movements.The aim of this paper is to use notches as sea level indicators to identify formershoreline positions in the area of Theologos and to show that their presence anddevelopment is associated with vertical movements of possible coseismic origin.In Section 2 the genesis of notch shapes is discussed, while in Section 3a briefpresentation of the geological setting and some archaeological and seismologicalinformation of the study area is presented. The methodology used is summarized inSection 4, while the main results obtained are presented and discussed in Sections 5and 6.2

Corrigendum to "Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)" published in Clim. Past, 4, 107–124, 2008

Fig. 4. From top to bottom. Pollen zones. Alkenone based sea surface temperatures (red line, upper right axis). Accumulation rates of total pollen per cm per a (green line, upper left axis). Total pollen concentration (green line) and Podocarpus pollen concentration (blue line) per ml sediment (middle right axis). Sedimentation rates in m per ka (shaded, lower left axis) and rates of sea-level change (line, lower right axis) after Fleming et al. (1998). Fig. 4. From top to bottom. Pollen zones. Alkenone based sea surface temperatures (red line, upper right axis). Accu ulation rates of total pollen per cm2 per a (green line, upper left axis). Total pollen concentration (green line) and Podocarpus pollen concentration (blue line) per ml sediment (middle right axis). Sedimentation rates in m per ka (shaded, lower left axis) and rates of sea-level change (line, lower right axis) after Fleming et al. (1998).

Sea level change in the Gulf of Thailand from GPS-corrected tide gauge data and multi-satellite altimetry

Investigation of long-term tidal data and short-term altimetry measurements reveals that sea level in the Gulf of Thailand is rising significantly faster than global average rates. Upward land motion detected from repeated precise GPS campaign measurements is used to correct the apparent sea level change from tide gauge, yielding absolute long-term trends as follows: Sattahip (1942–2004) 5.0 ± 1.3 mm/yr, Ko Sichang (1940–1999) 4.5 ± 1.3 mm/yr and Ko Mattaphon (1964–2004) 4.4 ± 1.1 mm/yr. Dual-crossover minimization of multi-mission altimetry data covering the 1993–2009 period reveals the following absolute sea level rates: Sattahip 4.8 ± 0.7 mm/yr, Ko Sichang 5.8 ± 0.8 mm/yr, Ko Lak 3.6 ± 0.7 mm/yr and Ko Mattaphon 3.2 ± 0.7 mm/yr. In other parts of the Gulf, the 1993–2009 rising rates are also in the range of 3 to 5.5 mm/yr. In the entire Gulf we don't find any evidence of sea level falling. At Ko Lak where the collocation of Topex-class altimetry ground track and the tidal station is extremely good, vertical land motion derived from the difference of sea level change rates detected by altimetry and tidal data is used to correct the apparent rate, yielding an absolute long-term (1940–2004) rate of 3.0 ± 1.5 mm/yr. The differences between the altimetry-based rates and the absolute tide gauge sea level trends can be explained by interannual variations like ENSO and decadal variations due to solar activity and lunar nutation. Post-2004 tidal data have been treated separately in our study because reliable values of region-wide vertical co-seismic displacements and post-seismic velocities caused by the 2004 Mw9.2 Sumatra-Andaman earthquake are still not accurately known. Exclusion of these data will not significantly change the determined long-term absolute sea level change rates because of the relatively short time span of post-earthquake sea level data compared to the complete tidal record. The impact of fast rising sea level combined with high rates of post-seismic downward crustal motions as indicated by GPS data makes coastal areas and river estuaries along the Gulf of Thailand highly vulnerable to flooding, particularly the low-lying city of Bangkok.

Minimum time span of TOPEX/Poseidon, Jason-1 and Jason-2 global altimeter data to detect a significant trend and acceleration in sea level change

The present study aims to estimate a minimum time span of the global mean sea level time series (from TOPEX/Poseidon, Jason-1 and Jason-2 satellite altimetry) which is sufficient to detect a statistically meaningful trend in global sea level variation. In addition, the objective of this paper is also to seek a minimum time span required to detect a significant acceleration in sea level change.Detecting a trend is based upon the Cox–Stuart statistical test. In order to make the analysis representative a stepwise procedure is proposed. The input global mean sea level time series is divided into shorter data sets (blocks) of dissimilar lengths. First, a length of block is chosen and the test is performed for the first truncated time series of a fixed length. Subsequently, the block is moved one step forward in each iteration. This produces the dissimilar data sets of the same length. The procedure is repeated for blocks of greater lengths and for each step the Cox–Stuart test is applied. The procedure makes the inference independent of the starting data epoch. Considering the set S={0.002,0.004,…,0.1} of significance levels, the test is applied to compute the probability of trend detection. Detecting an acceleration is based on the same procedure, however, applied to the differenced global mean sea level time series.We infer that the trend in the global mean sea level time series (January 1993–April 2010) corrected for the global isostatic adjustment can be detected for all significance levels from the set S with the probability close to 1 after 110 satellite cycles (approximately 2.99 years). The corresponding estimate based on the data without correcting for the global isostatic adjustment is equal to 114 satellite cycles (approximately 3.09 years). Over the majority of the study period it is impossible to detect any acceleration in sea level rise. However, for the time spans of approximately 400 and 500 satellite cycles an acceleration may be detected with probability of approximately 0.4. These specific time spans correspond to the periods with reduced rates of sea level change.

Quantifying rates of change in ocean conditions with implications for timing of sea level change

The importance of southern hemisphere driven climate change is increasingly recognized in paleoclimate research. This is in particular relevant with regard to the rate of climate change initiated in the southern hemisphere and the phasing thereof compared to climate variability elsewhere. Here, we use previously published benthic oxygen isotope data from two deep sea sediment cores from the deep N-Atlantic and the intermediate depth Indian Ocean to quantify rates of oceanic change at the millennial-scale. The oxygen isotope data represent an integrated signal of temperature and global sea level changes. At both locations the sea surface ocean records strongly resemble Greenland climate change. When used to synchronize these surface ocean records with the GISP2 ice core chronology we show that the highest rates of change in the benthic oxygen isotope records, occur during late marine isotope stage 5 (MIS 5), MIS 3 and the last deglaciation, whilst generally modest rates of change prevail during the full glacial conditions of MIS 2. The synchronous variation of oceanic rates of change and Antarctic climate history suggests that the benthic oxygen isotope records from the glacial deep N-Atlantic and the intermediate Indian Ocean reflect variations in southern sourced Antarctic Bottom Water (AABW) and Glacial Antarctic Intermediate Water (GAAIW) respectively. Millennial-scale temperature variations in GAAIW are larger than in AABW. The repeated rapid heat storage in GAAIW during northern hemisphere cold phases points to an important role of GAAIW, potentially acting as an energy buffer, maintaining the pole-to-pole climate imbalance as part of the bi-polar seesaw. Combining the benthic oxygen isotope records with independent sea level records shows a pulsed sea level rise history during the deglaciation with conservative estimates of peak rates change of about ~ 2 m/100 yr. Similar rates of sea level change occurred during most Heinrich Events.

Analyzing niche stability and biogeography of Late Ordovician brachiopod species using ecological niche modeling

Gauging the potential impacts of environmental change on the geographic distributions of species is a central area of modern biogeographic analysis, often involving complex models of species–environment interactions. The geographic distribution of fossil species can also provide a framework to test the impact of environmental change on biogeography and ecological niches of species, yet few paleontological analyses have attacked this question in deep time. Herein we present a quantitative biogeographic analysis to examine the stability of ecological niches and geographic ranges of rhynchonelliform brachiopods during an interval of sea level change preserved in Upper Ordovician strata of the Cincinnati Arch.The intensive sampling, excellent preservation, and numerous prior paleoecological and sedimentological analyses within the tri-state region of Kentucky, Indiana, and Ohio provide a robust framework for detailed paleobiogeographic study. Quantitative biogeographic modeling methods incorporating GIS (Geographic Information Systems) are utilized in order to spatially analyze the geographic ranges of brachiopod species of the Corryville and Mt. Auburn Formations of the C3 (uppermost Maysvillian) depositional sequence.This study employs the ecological niche modeling program GARP (Genetic Algorithm using Rule-set Prediction) to predict the geographic distribution of eight brachiopod species during three time slices within the C3 sequence. This method estimates a species’ geographic range by modeling the ecological niche of the species based on a set of known species occurrence data coupled with environmental data inferred from sedimentologic proxies. Once environmental tolerances for a species are modeled; the species is predicted to occur wherever its preferred set of environmental conditions occurs within the study region.Distributional patterns were reconstructed for three time slices during the C3 sequence. Recovered range predictions were quantitatively analyzed for evidence of temporal range changes. Results indicate that average species range within the study area decreased and species tracked their preferred niche with high fidelity during the transition from the early to middle portions of the C3 depositional sequence, an interval of rapid relative sea level change. However, during the transition from the middle to late portions of the sequence, gradual shallowing within the basin and development of discontinuous habitat patches correlates with niche evolution of five of the eight species modeled. The average area a species occupied within the basin increased during this interval, but there is a mixed response including both increases and decreases in range size within the study group. In general, the species that exhibit niche evolution increased their geographic range size while those that continue to track their niche with high fidelity experience a decrease in geographic range size. During the latter half of the C3 sequence, previously continuous habitats become fragmented, thereby isolating individual populations and providing a mechanism for niche evolution. The rate of sea level change and the corresponding fragmentation of previously continuous habitats into isolated patches appear to be the primary controls on both mean geographic range size and relative degree of niche evolution.

The impact of Late Quaternary glacio-eustasy and tectonics on sequence development: evidence from both uplifting and subsiding settings in Italy

Terra Nova, 22, 324–329, 2010 Abstract The contributions of eustasy and tectonics to the development of stratigraphic sequences are commonly hard to discern, and this has been a controversial topic that is still being debated. New data are therefore necessary to improve our understanding of the factors that govern sedimentary cyclicity. Data from the subsiding Venice and the uplifting Crotone areas in Italy allow the recognition of the different effects of Late Quaternary glacio-eustatic changes and regional tectonics on sequence architecture at different temporal scales. Shallow-marine small-scale sequences linked to short-term glacio-eustatic changes at the scale of the marine isotope substage cyclicity (104 years) show features that developed irrespective of the local conditions of subsidence or uplift, such as a modest thickness, a similar organization of facies and thin transgressive deposits. In contrast, lower frequency composite sequences at the scale of 105 years show strongly different architectures and stacking patterns depending on the regional tectonic context: downstepping in uplifting areas and aggradational in subsiding areas. The present results, therefore, highlight that only the architecture of small-scale sequences showing a periodicity of about 20 and 40 ka appears to be dominated by the glacio-eustatic variable, because of the very high rates of sea-level change characterizing the substage cyclicity, which overprints the regional tectonic signal.

Deglacial history of the West Antarctic Ice Sheet in the Weddell Sea embayment: Constraints on past ice volume change

The retreat history of the West Antarctic Ice Sheet (WAIS) since the Last Glacial Maximum is important for understanding the process of rapid deglaciation, constraining models that seek to predict the future trajectory of the ice sheet, and for estimating rates of sea-level change. Here we report new glacial geologic data from the southwestern Weddell Sea embayment that demonstrate that this part of the WAIS was thinner than previously suggested, and that there was progressive thinning of the ice sheet by 230–480 m since ca. 15 ka. We use geomorphological data and a numerical ice sheet model to reconstruct the ice sheet in the Weddell Sea at the Last Glacial Maximum. The volume of this ice would have added between 1.4 and 2.0 m to postglacial sea-level rise and would not have been sufficient to contribute significantly to meltwater pulse 1A, a rapid rise in sea level ∼14,200 yr ago.