Ice volume estimates from ground-penetrating radar surveys, western Nordenski��ld Land glaciers, Svalbard

As part of ongoing work within the SvalGlac project aimed to obtain a reliable estimate of the total ice volume of Svalbard glaciers and their potential contribution to sea level rise, in this contribution we present volume calculations, with detailed error estimates, for ten glaciers on western Nordenski��ld Land, central Spitsbergen, Svalbard. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 1999-2012, all of them except one within 2010-2012. The total area and volume of the ensemble are 113.38��0.09 km2 and 10.439��0.185 km3, respectively, while the individual areas, volumes and average ice thickness lie within 2.5-49.1 km2, 0.08-5.48 km3 and 29-108 m, respectively. The maximum recorded ice thickness, 265��15 m, corresponds to Fridtjovbreen, which has also the largest average thickness (108��1m). Available empirical formulae for Svalbard glaciers overestimate the total volume of these glaciers by 24% with respect to our calculation. On the basis of the pattern of scattering in the radargrams, we also analyse the hydrothermal structure of these glaciers. Nine out of ten are polythermal, while only one is entirely cold.

Ice volume estimates from ground-penetrating radar surveys, Wedel Jarlsberg Land glaciers, Svalbard

One of the aims of the SvalGlac project is to obtain an improved estimate, with reliable error estimates, of the volume of Svalbard glaciers and their potential contribution to sea level rise. As part of this work, we present volume calculations, with detailed error estimates, for eight glaciers on Wedel Jarlsberg Land, southern Spitsbergen, Svalbard. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 2004-2011. The total area and volume of the ensemble are 502.9��18.6 km2 and 80.72��2.85 km3, respectively. Excluding Ariebreen (a tiny glacier, menor que 0.4 km2 in area), the individual areas, volumes and average ice thickness lie within 4.7-141.0 km2, 0.30-25.85 km3 and 64-183 m, respectively. The maximum recorded ice thickness, ca. 619��13 m, is found in Austre Torellbreen. To estimate the ice volume of small non-echo-sounded tributary glaciers, we used a function providing the best fit to the ice thickness along the centre line of a collection of such tributaries where echo-soundings were available, and assuming parabolic cross-sections. We did some tests on the effect on the measured ice volumes of the distinct radio-wave velocity (RWV) of firn as compared to ice, and cold versus temperate ice, concluding that the changes in volume implied by such corrections were within the error bounds of our volume estimate using a constant RWV for the entire glacier inferred from common mid-point measurements on the upper ablation area.

On the steric and mass-induced contributions to the annual sea level variations in the Mediterranean Sea

The sea level variation (SLVtotal) is the sum of two major contributions: steric and mass-induced. The steric SLVsteric is that resulting from the thermal and salinity changes in a given water column. It only involves volume change, hence has no gravitational effect. The mass-induced SLVmass, on the other hand, arises from adding or subtracting water mass to or from the water column and has direct gravitational signature. We examine the closure of the seasonal SLV budget and estimate the relative importance of the two contributions in the Mediterranean Sea as a function of time. We use ocean altimetry data (from TOPEX/Poseidon, Jason 1, ERS, and ENVISAT missions) to estimate SLVtotal, temperature, and salinity data (from the Estimating the Circulation and Climate of the Ocean ocean model) to estimate SLVsteric, and time variable gravity data (from Gravity Recovery and Climate Experiment (GRACE) Project, April 2002 to July 2004) to estimate SLVmass. We find that the annual cycle of SLVtotal in the Mediterranean is mainly driven by SLVsteric but moderately offset by SLVmass. The agreement between the seasonal SLVmass estimations from SLVtotal ��� SLVsteric and from GRACE is quite remarkable; the annual cycle reaches the maximum value in mid-February, almost half a cycle later than SLVtotal or SLVsteric, which peak by mid-October and mid-September, respectively. Thus, when sea level is rising (falling), the Mediterranean Sea is actually losing (gaining) mass. Furthermore, as SLVmass is balanced by vertical (precipitation minus evaporation, P���E) and horizontal (exchange of water with the Atlantic, Black Sea, and river runoff) mass fluxes, we compared it with the P���E determined from meteorological data to estimate the annual cycle of the horizontal flux.

Sedimentology at the continental margin of the southern Weddell Sea

During four expeditions with RV "Polarstern" at the continental margin of the southern Weddell Sea, profiling and geological sampling were carried out. A detailed bathymetric map was constructed from echo-sounding data. Sub-bottom profiles, classified into nine echotypes, have been mapped and interpreted. Sedimentological analyses were carried out on 32 undisturbed box grab surface samples, as well as on sediment cores from 9 sites. Apart from the description of the sediments and the investigation of sedimentary structures on X-radiographs the following characteristics were determined: grain-size distributions; carbonate and Corg content; component distibutions in different grain-size fractions; stable oxygen and carbon isotopes in planktic and, partly, in benthic foraminifers; and physical properties. The stratigraphy is based On 14C-dating, oxygen isotope Stages and, at one site, On paleomagnetic measurements and 230Th-analyses The sediments represent the period of deposition from the last glacial maximum until recent time. They are composed predominantly of terrigenous components. The formation of the sediments was controlled by glaciological, hydrographical and gravitational processes. Variations in the sea-ice coverage influenced biogenic production. The ice sheet and icebergs were important media for sediment transport; their grounding caused compaction and erosion of glacial marine sediments on the outer continental shelf. The circulation and the physical and chemical properties of the water masses controlled the transport of fine-grained material, biogenic production and its preservation. Gravitational transport processes were the inain mode of sediment movements on the continental slope. The continental ice sheet advanced to the shelf edge and grounded On the sea-floor, presumably later than 31,000 y.B.P. This ice movement was linked with erosion of shelf sediments and a very high sediment supply to the upper continental slope from the adiacent southern shelf. The erosional surface On the shelf is documented in the sub-bottom profiles as a regular, acoustically hard reflector. Dense sea-ice coverage above the lower and middle continental slope resulted in the almost total breakdown of biogenic production. Immediately in front of the ice sheet, above the upper continental slope, a <50 km broad coastal polynya existed at least periodically. Biogenic production was much higher in this polynya than elsewhere. Intense sea-ice formation in the polynya probably led to the development of a high salinity and, consequently, dense water mass, which flowed as a stream near bottom across the continental slope into the deep sea, possibly contributing to bottom water formation. The current velocities of this water mass presumably had seasonal variations. The near-bottom flow of the dense water mass, in combination with the gravity transport processes that arose from the high rates of sediment accumulation, probably led to erosion that progressed laterally from east to West along a SW to NE-trending, 200 to 400 m high morphological step at the continental slope. During the period 14,000 to 13,000 y.B.P., during the postglacial temperature and sea-level rise, intense changes in the environmental conditions occured. Primarily, the ice masses on the outer continental shelf started to float. Intense calving processes resulted in a rapid retreat of the ice edge to the south. A consequence of this retreat was, that the source area of the ice-rafted debris changed from the adjacent southern shelf to the eastern Weddell Sea. As the ice retreated, the gravitational transport processes On the continental slope ceased. Soon after the beginning of the ice retreat, the sea-ice coverage in the whole research area decreased. Simultaneously, the formation of the high salinity dense bottom water ceased, and the sediment composition at the continental slope then became influenced by the water masses of the Weddell Gyre. The formation of very cold Ice Shelf Water (ISW) started beneath the southward retreating Filchner-Ronne Ice Shelf somewhat later than 12,000 y.B.P. The ISW streamed primarily with lower velocities than those of today across the continental slope, and was conducted along the erosional step on the slope into the deep sea. At 7,500 y.B.P., the grounding line of the ice masses had retreated > 400 km to the south. A progressive retreat by additional 200 to 300 km probably led to the development of an Open water column beneath the ice south of Berkner Island at about 4,000 y.B.P. This in turn may have led to an additional ISW, which had formed beneath the Ronne Ice Shelf, to flow towards the Filcher Ice Shelf. As a result, increased flow of ISW took place over the continental margin, possibly enabling the ISW to spill over the erosional step On the upper continental slope towards the West. Since that time, there is no longer any documentation of the ISW in the sedimentary Parameters on the lower continental slope. There, recent sediments reflect the lower water masses of the Weddell Gyre. The sea-ice coverage in early Holocene time was again so dense that biogenic production was significantly restricted.

Distribution of grain size and clay minerals in surface sediments of the Kara Sea (Fig 4, 5)

In this paper, we summarize data on terrigenous sediment supply in the Kara Sea and its accumulation and spatial and temporal variability during Holocene times. Sedimentological, organic-geochemical, and micropaleontological proxies determined in surface sediments allow to characterize the modern (riverine) terrigenous sediment input. AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 cal kyr BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge. Based on sediment thickness charts, echograph profiles and sediment core data, we estimate an average Holocene (0-11 cal kyr BP) annual accumulation of 194,106 t/yr of total sediment for the whole Kara Sea. Based on late Holocene (modern) sediment accumulation in the estuaries, probably 12,106 t/yr of riverine suspended matter (i.e. about 30% of the input) may escape the marginal filter on a geological time scale and is transported onto the open Kara Sea shelf. The high-resolution magnetic susceptibility record of a Yenisei core suggests a short-term variability in Siberian climate and river discharge on a frequency of 300-700 yr. This variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the High Northern Latitudes over the last decades, such as the NAO/AO pattern. A major decrease in MS values starting near 2.5 cal kyr BP, being more pronounced during the last about 2 cal kyr BP, correlates with a cooling trend over Greenland as indicated in the GISP-2 Ice Core, extended sea-ice cover in the North Atlantic, and advances of glaciers in western Norway. Our still preliminary interpretation of the MS variability has to be proven by further MS records from additional cores as well as other high-resolution multi-proxy Arctic climate records.

Sedimentological and geophysical investigation of sediment cores from the Amundsen Sea

Ice loss from the marine-based, potentially unstable West Antarctic Ice Sheet (WAIS) contributes to current sea-level rise and may raise sea level by up to 3.3 to 5 meters in the future. Over the past few decades, glaciers draining the WAIS into the Amundsen Sea Embayment (ASE) have shown accelerated ice flow, rapid thinning and grounding-line retreat. However, the long-term context of this ice-sheet retreat is poorly constrained, limiting our ability to accurately predict future WAIS behaviour. Here we present a new chronology for WAIS retreat from the inner continental shelf of the eastern ASE based on radiocarbon dates from three marine sediment cores. The ages document a retreat of the grounding line to within ~93 km of its modern position before 11.7��0.7 kyr BP (thousand years before present). This early deglaciation is consistent with ages for grounding-line retreat from the western ASE. Our new data demonstrate that, other than in the Ross Sea, WAIS retreat in the ASE has not continued progressively since the Last Glacial Maximum. Furthermore, our results suggest that the grounding-line position in the ASE was predominantly stable throughout the Holocene, and that any episodes of fast retreat similar to that observed today must have been short-lived. Alternatively, today's rapid retreat was unprecedented during the Holocene. Therefore, the current ice loss must originate in recent changes in regional climate, ocean circulation or ice-sheet dynamics. Incorporation of these results into models is essential to produce robust predictions of future ice-sheet change and its contribution to sea-level rise.

Physical and chemical properties, 14C ages and palynology of sediment cores from the Western Baltic Sea

Sea level related radiocarbon, palynological and stratigraphical data from sediment cores in the Western Baltic have been tested against the existing sea level curves for the region. The relative sea level rise curves for the beginning of the Holocene show no significant deviations between the Kiel, Mecklenburg und L��beck Bays and hence do not support the previously reported differences in the averaged regional subsidence rates for this time interval. Local subsidence and upheaval due to salt tectonics probably played a greater role than previously suspected in the region. The sea level possibly stagnated around -28 m during the early Holocene before rising very rapidly to -14 m. The submarine terraces at -30 m and perhaps also at -27 m were formed during the lacustrine phase of the Western Baltic when the water levels were controlled by the main thresholds in the Great Belt.

(Table S1) Age determination of sediment cores of the Gulf of Alaska

Oxygen isotope data from planktonic and benthic foraminifera, on a high-resolution age model (44 14C dates spanning 17,400 years), document deglacial environmental change on the southeast Alaska margin (59��33.32'N, 144��9.21'W, 682 m water depth). Surface freshening (i.e., d18O reduction of 0.8 per mil) began at 16,650 �� 170 cal years B.P. during an interval of ice proximal sedimentation, likely due to freshwater input from melting glaciers. A sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14,790 �� 380 cal years B.P. Abrupt warming and/or freshening of the surface ocean (i.e., additional d18O reduction of 0.9 per mil) coincides with the B��lling Interstade of northern Europe and Greenland. Cooling and/or higher salinities returned during the Aller��d interval, coincident with the Antarctic Cold Reversal, and continue until 11,740 �� 200 cal years B.P., when onset of warming coincides with the end of the Younger Dryas. An abrupt 1 per mil reduction in benthic d18O at 14,250 �� 290 cal years B.P. likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater, a regional megaflood event, or brine formation associated with sea ice. Two laminated opal-rich intervals record discrete episodes of high productivity during the last deglaciation. These events, precisely dated here at 14,790 �� 380 to 12,990 �� 190 cal years B.P. and 11,160 �� 130 to 10,750 �� 220 cal years B.P., likely correlate to similar features observed elsewhere on the margins of the North Pacific and are coeval with episodes of rapid sea level rise. Remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia.

(Appendix 1) Coral analysis and isostatic rebound effects from different Holes of IODP Expedition 310

Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the B��lling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A.

(Table 1) Age determination and isotopic signature of last glacial Patagonian caly/silt

Ice cores provide a record of changes in dust flux to Antarctica, which is thought to reflect changes in atmospheric circulation and environmental conditions in dust source areas (Forster et al., 2007; Diekmann et al. 2000, doi:10.1016/S0031-0182(00)00138-3; Winckler et al., 2008, doi:10.1126/science.1150595; Reader et al., 1999, doi:10.1029/1999JD900033; Mahowald et al., 1999, doi:10.1029/1999JD900084; Petit et al., 1999, doi:10.1038/20859; 1990, doi:10.1038/343056a0 Delmonte et al., 2009, doi:10.1029/2008GL033382; Lambert et al., 2008, doi:10.1038/nature06763). Isotopic tracers suggest that South America is the dominant source of the dust (Grousset et al., 1992, doi:10.1016/0012-821X(92)90177-W; Basile et al., 1997, doi:10.1016/S0012-821X(96)00255-5; Gaiero et al., 2007, doi:10.1016/j.chemgeo.2006.11.003), but it is unclear what led to the variable deposition of dust at concentrations 20-50 times higher than present in glacial-aged ice (Petit et al., 1990, doi:10.1038/343056a0; Lambert et al., 2008, doi:10.1038/nature06763). Here we characterize the age and composition of Patagonian glacial outwash sediments, to assess the relationship between the Antarctic dust record from Dome C (refs Lambert et al., 2008, doi:10.1038/nature06763; Wolff et al., 2006, doi:10.1038/nature04614) and Patagonian glacial fluctuations (Sugden et al., 2005; McCulloch et al., 2005, doi:10.1111/j.0435-3676.2005.00260.x; Kaplan et al., 2008, doi:10.1016/j.quascirev.2007.09.013) for the past 80,000 years. We show that dust peaks in Antarctica coincide with periods in Patagonia when rivers of glacial meltwater deposited sediment directly onto easily mobilized outwash plains. No dust peaks were noted when the glaciers instead terminated directly into pro-glacial lakes. We thus propose that the variable sediment supply resulting from Patagonian glacial fluctuations may have acted as an on/off switch for Antarctic dust deposition. At the last glacial termination, Patagonian glaciers quickly retreated into lakes, which may help explain why the deglacial decline in Antarctic dust concentrations preceded the main phase of warming, sea-level rise and reduction in Southern Hemisphere sea-ice extent (Wolff et al., 2006, doi:10.1038/nature04614).

Conference on Continental Margin Mass-wasting and Pleistocene Sea-level Changes, August 13-15, 1980 /

Mode of access: Internet.

Surface Elevation Change Processes in the Snohomish River Estuary, Washington

Estuaries provide crucial ecosystem functions and contain significant socio-economic value. Within Washington State, estuaries supply rearing habitat for juvenile salmon during their transition period from freshwater to open sea. In order to properly manage wetland resources and restore salmon habitat, the mechanisms through which estuaries evolve and adapt to pressures from climate change, most notably eustatic sea level rise, must be understood. Estuaries maintain elevation relative to sea level rise through vertical accretion of sediment. This report investigates the processes that contribute to local surface elevation change in the Snohomish Estuary, conveys preliminary surface elevation change results from RTK GPS monitoring, and describes how surface elevation change will be monitored with a network of RSET-MH���s. Part of the tidal wetlands within the Snohomish River Estuary were converted for agricultural and industrial purposes in the 1800���s, which resulted in subsidence of organic soils and loss of habitat. The Tulalip Tribes, the National Oceanic and Atmospheric Administration (NOAA), Northwest Indian Fisheries Commission (NWIFC), and the Environmental Protection Agency (EPA) are conducting a large-scale restoration project to improve ecosystem health and restore juvenile salmon habitat. A study by Crooks et al. (2014) used 210Pb and carbon densities within sediment cores to estimate wetland re-building capacities, sediment accretion rates, and carbon sequestration potential within the Snohomish Estuary. This report uses the aforementioned study in combination with research on crustal movement, tidal patterns, sediment supply, and sea level rise predictions in the Puget Sound to project how surface elevation will change in the Snohomish Estuary with respect to sea level rise. Anthropogenic modification of the floodplain has reduced the quantity of vegetation and functional connectivity within the Snohomish Estuary. There have been losses up to 99% in vegetation coverage from historic extents within the estuary in both freshwater and mesohaline environments. Hydrographic monitoring conducted by NOAA and the Tulalip Tribe shows that 85% of the historic wetland area is not connected to the main stem of the Snohomish (Jason Hall 2014, unpublished data, NOAA). As vegetation colonization and functional connectivity of the floodplains of the Snohomish estuary is re-established through passive and active restoration, sediment transport and accretion is expected to increase. Under the Intergovernmental Panel on Climate Change (IPCC) ���medium- probability��� scenario sea level is projected to rise at a rate of 4.28 mm/year in the Puget Sound. Sea level rise in the Snohomish Estuary will be exacerbated from crustal deformation from subsidence and post-glacial rebound, which are measured to be -1.4 mm/year and -0.02 mm/year, respectively. Sediment accretion rates calculated by Crooks et al. (2014) and RTK GPS monitoring of surface elevation change of the Marysville Mitigation site from 2011-2014 measured vertical accretion rates that range from -48-19 mm/year and have high spatial variability. Sediment supply is estimated at 490 thousand tons/year, which may be an under-estimate because of the exclusion of tidal transport in this value. The higher rates of sediment accretion measured in the Snohomish Estuary suggest that the Snohomish will likely match or exceed the pace of sea level rise under ���medium-probability��� projections. The network of RSET-MH instruments will track surface elevation change within the estuary, and provide a more robust dataset on rates of surface elevation change to quantify how vertical accretion and subsidence are contributing to surface elevation change on a landscape scale.

A high-precision record of mid-late Holocene sea-level events from emergent coral pavements in the Houtman Abrolhos Islands, southwest Australia

Early work on sea-levels in southwest Australia claimed to recognise a Holocene sea-level highstand which was not seen in better known sea-level records elsewhere at the time. More recent work has confirmed that a mid-Holocene highstand Occurred about 6 kyr ago. As new data on oscillating sea-levels from the region have recently been published, a high continuity, precisely dated and accurately surveyed record was obtained from emergent coral pavements in the leeward Houtman Abrolhos Islands (Serventy Island), a tectonically stable region from where good-quality Holocene sea-level data have been previously obtained from corals. From the mid-Holocene highstand ca. 7 U/Th kyr ago, sea-level declined linearly during the remainder of the Holocene as the carbonate platform prograded leewards. Hydro-isostatic controls are probably significant in the record. (c) 2005 Elsevier Ltd and INQUA. All rights reserved.