PP51A-1473
The Potential of Uranium-Series Disequilibrium in Marine and Lacustrine Diatom Frustules as a Tool for Geochronological and Paleoenvironmental Studies
Accurate age dating of deep-sea sediment records from the polar region remains one of the major challenging issues in paleoceanographic and paleoclimatologic studies. As diatom is ubiquitous in aquatic systems, in particular in cold waters of the polar region, this study seeks to explore the utilities of uranium- series disequilibrium in diatom frustules as a chronometer for absolute age dating and/or as a proxy for paleo-environmental studies. In the uranium series, uranium-238, with a half-life of 4.468 billion year, decays to a stable nuclide lead-206 through a series of shorter-lived radionuclides. Uranium-238 and all of its daughter nuclides will achieve secular equilibrium on a time scale of about one million years in an igneous rock. Disequilibrium between the daughter and parent nuclides would occur in aquatic environments, such as in oceans and lakes, as a result of various naturally-occurring physical/chemical processes. This study shows that diatom acquires its uranium isotope composition from its ambient seawater, creating significant radioactive disequilibrium between uranium and its daughter nuclides in diatom frustules. This salient feature makes diatom frustules very useful for absolute age dating as well as for assessing the past changes of many geophysical and geochemical processes in the ocean and on the continents.
PP51A-1474
Mackenzie Glacial Outburst Floods into the Arctic Ocean 13,000–10,000 Years ago
An unconformity with an area of at least 9400 km2 and a relief of about 100 m in the eastern Beaufort continental shelf and adjacent coastlands near the Mackenzie Delta is attributed to fluvial erosion during deglaciation of the northwest Laurentide Ice Sheet. On northeast Richards Island, the unconformity is overlain by a fluvial gravel or gravelly lag of pebble to boulder-size material. Optical dating of eolian sand above and below the unconformity constrains erosion and deposition to between about 13.0 and 10.1 ka. Additional optical dates from fluvial sand above gravel indicate an age of about 11.8 ka. If the active margin of the Laurentide Ice Sheet had retreated nearly 600 km southeast of Richards Island by 13 ka, as shown in the Dyke et al. (2003) reconstruction of deglaciation, then a local source of glacial meltwater is discounted. Instead, the fluvial activity was likely associated with outburst flooding from distant glacial lakes into the Arctic Ocean. An earlier episode of flooding shortly after about 13 ka possibly coincided with the onset of the Younger Dryas, and a later episode between about 11.8 ka and 10.1 ka possibly coincided with the onset of the Pre-Boreal Oscillation at about 11.3 ka. The new geological evidence from the Mackenzie Delta region supports recent proposals that massive discharges of glacial meltwater issued northward along the Mackenzie River during deglaciation of the Laurentide Ice Sheet.
PP51A-1475
Deglaciation of the James Bay Lowlands and Northern Abitibi: Insights on Late-Glacial Ice Readvances and Drainage of Glacial Lake Ojibway
Deglaciation in the James Bay region was marked by the scission of the Laurentide ice sheet margin into the Hudson dome to the west and the New-Quebec dome to the east, which subsequently retreated northward, in contact with the waters of glacial Lake Ojibway. Previous work based on air photo-interpretation and field observations indicate that ice retreat in the region was highly dynamic, with the occurrence of at least three ice readvances into the basin of Lake Objiway prior to the final deglaciation, and the incursion of the post- glacial Tyrrell Sea at ~8 ka (Hardy, 1976). Our investigations of stratigraphic sections exposed along the Harricana, Nottaway, Broadback, and Rupert rivers in the lowlands of Quebec indicate that only part of these events are preserved in these sedimentary sequences. The base of the late-glacial sequence generally consists of a carbonate-bearing clayey readvance till that lies on older tills of the last glacial cycle, or truncate Lake Ojibway glaciolacustrine sediments. None of the sections showed more than one till of the three (Cochrane I, Rupert, Cochrane II) readvances documented in the region. Nonetheless, an extensive Ojibway sequence located just south from the lowlands shows three intervals with significant increases in detrital carbonate and coarsening of the varve sequence that can be linked with these late-glacial surges. In the lowlands, the readvance till is commonly capped by a thick sequence of Ojibway varves. The contact between the glaciolacustrine sediments and the overlying Tyrrell Sea marine deposits is marked by a ~50 cm-thick horizon composed at the bottom of thinly laminated reddish and grey silt beds containing abundant rounded clay balls, overlain by coarser silts and fine sands with disseminated clasts. This horizon is here interpreted to reflect the abrupt drainage of Lake Ojibway. Recent radiocarbon dating of mollusks and foraminifers from the uppermost part of this horizon yielded ages of ~7.7 ka and ~8.0 ka. These results thus identify the James Bay axis as an important pathway through which glacial Lake Ojibway waters drained shortly before the marine incursion. Further south, in the Abitibi region, the flat-lying Ojibway clay plains show former lake shores (wave-cut benches) incised into the glaciolacustrine sediments, thereby suggesting abrupt lowering of the Ojibway lake level (Thibaudeau and Veillette, 2005). Nearby stratigraphic exposures of varved clays contain a ~30-40 cm-thick bed consisting of massive silts and fine sands that also suggests some kind of lowering and drainage of the lake waters. The paleoecological content of these coarser horizons and bounding glaciolacustrine clays are currently being investigated for further analyses and radiocarbon dating. The results should provide additional information on the timing of these low lake levels, and their possible link with the drainage horizon documented in the James Bay lowlands.
PP51A-1476
Arctic Ocean's freshwater budget estimate: planktonic foraminiferal Mg/Ca and Ba/Ca approach
Studies over the last decade suggest that the summer Arctic sea-ice may disappear by 2020, a faster rate than most modelers anticipated. Such a forecast is important to the freshwater budget around the circum- Arctic as well as to the freshwater fluxes through the Bering and Fram Straits. To assess the Arctic Ocean freshwater delivery to the site of Meridional Overturning Circulation, the study of past changes in such fluxes and summer sea-ice is required. The last interglacial can be used as an analog for the late and post Holocene periods. Estimating reliable sea-surface temperatures based on Mg/Ca in Neogloboquadrina pachyderma (sinistral) may not be possible in the Arctic Ocean because the lack of sensitivity of Mg/Ca at low temperatures. Nevertheless, variations in Mg/Ca compared to δ18O will characterize relative temperature changes. The Ba/Ca in planktonic foraminifera has recently been shown as a proxy for freshwater input. Because North American Arctic rivers have 5 times higher dissolved Ba concentration than Eurasian rivers, measuring Ba/Ca in planktonic foraminifera from the Mendeleev and Lomonosov Ridges will help to delineate the relative discharge between the American and Eurasian rivers. Mg/Ca and Ba/Ca were analyzed in N. pachyderma (s) from fifteen core tops from the Arctic Ocean and selected depth intervals from Marine Isotope Stages 3.1. 3.3, and 5.1 from core HLY0503-08JPC, retrieved during the HOTRAX'05 expedition from the Mendeleev Ridge (79.356°N, 172.301°W) at 2,792 m water depth.
PP51A-1477
Boulder Recycling, Moraine Degradation, and Their Effects on Cosmogenic Exposure Dating of Moraines
Recent exposure dates from the Gurreholm valley in Greenland suggest that the ice sheet advanced several times during late glacial to early Holocene time and during the Little Ice Age. Here, we demonstrate that this data set has a distinctly different structure from a recent set of exposure dates from the Waiho Loop moraine in New Zealand. Using geomorphic process modeling, we explain this difference in terms of the dominant geomorphic process at each field site. Our model treats two processes, boulder recycling and moraine degradation. In boulder recycling, previously exposed boulders are incorporated into new moraines. The degree to which any given boulder reflects the true age of a new moraine depends on both the predepositional exposure time of the boulder and how much the boulder was rotated from its original orientation by glacial transport. Where moraine degradation is the dominant process, previously shielded boulders are exposed to cosmic rays by the diffusive removal of material from the moraine's crest. In the model, these two processes yield distinctly different cumulative probability distributions of exposure ages. The cumulative density function for a set of exposure dates biased by boulder recycling rises rapidly, then levels off; the cumulative density function for exposure dates biased by moraine degradation rises more slowly at first, then increases. There is good agreement between model curves assuming moraine degradation and the observed distribution of exposure dates from the Waiho Loop. Similarly, the observed cumulative density functions for moraines in the Gurreholm valley resemble curves generated by the model for boulder recycling. Some mismatch remains between the observed and modeled cumulative density functions for the Gurreholm data sets. We expect this mismatch to be reduced as we improve the realism of the cosmic ray flux dependence on the angle from vertical in the model. In addition, preliminary fits of the model to the Gurreholm data set suggest that the prevalence of inheritance is correlated with the stratigraphic order of the moraines; the boulders on the youngest group of moraines contain the smallest amount of inherited nuclides, and the boulders on the oldest group of moraines contain the largest amount of inherited nuclides. This observation suggests that older advances removed preexposed boulders from the valley, leaving fewer boulders for subsequent advances to incorporate into their moraines.
PP51A-1478
Cosmogenic Nuclide Dating Results From Nordaustlandet Suggest Limited Late Weichselian Ice Sheet Coverage on Svalbard
AGU Abstract Svalbard is situated at the limb of the Barents Sea towards the Arctic Ocean, which makes it a key region for studies of the interaction of ice and the thermohaline ocean circulation in the climate system. In the last couple of years climate models pointed out that the location of freshwater input into the ocean system is crucial to the expected changes, not only the volume. Earth system models are tested against known former climate changes in the geological past. Developing useful data about the last ice sheet coverage and its geometry on Svalbard is essential for this purpose. While the freshwater events are known from some marine sediment cores, deglaciation events are not well documented in the source regions. Our knowledge of the last ice sheet coverage in the Svalbard region is based on only few sediment outcrops along the west coast of Svalbard, some on Barentsøya and Edgeøya and the marine sediment records. Until a more complete record from the central parts of Svalbard is established, it will not be possible to assess if the late Weichselian ice sheet was bigger than earlier Weichselian glaciations. Field work in Nordaustlandet during summer 2007 included preliminary mapping and sampling for cosmogenic nuclide dating of Prins Oscars Land east of Rijpfjorden and the inner part of Murchisonfjorden. We will present nineteen 10Be dates of bedrock and boulders that range from 117.9 kyr BP to 12.6 kyr BP. The oldest samples were taken from bedrock and evidently show inheritance of cosmogenic nuclides due to non-erosive cold-based glacier ice. The youngest samples might be interpreted as a local readvance during the Late Weichselian of a small ice cap located on Prins Oscars Land east of Rijpfjorden. Four samples of boulders in Murchisonfjord area cluster around 35 kyr and would rather suggest that Nordaustlandet experienced the maximum glaciation in mid-Weichselian and not in late Weichselian.
PP51A-1479
High Arctic Archives of Terrestrial Change in Svalbard Wetlands
High resolution records of change in terrestrial High Arctic environments are often limited by slow accumulation rates and the absence of material or conditions suitable for accurate chronologies. At several wetland sites in the inner fjords of western Svalbard we investigated organic deposits to assess the sensitivity of ecosystem carbon dynamics to past climate variation. These carbon rich wetlands contain by area about 26 to 61 kg C m-2 in deposits as thick as 1.4 m. Our radiocarbon evidence and the published literature show that sequestered carbon in Svalbard wetlands is typically of mid- to late-Holocene age. High resolution AMS radiocarbon measurements on fossil remains of individual plant species reveal a pattern of carbon sequestration that varied from multi-centennial periods of rapid accumulation, as high as about 35 g C m- 2 yr-1, to very slow or hiatus conditions that persisted for hundreds to thousands of years followed by renewed sequestration. Periods of strong carbon accumulation in the mid-Holocene and over the last thousand years capture High Arctic wetland conditions resolvable at the sub-decadal scale. This is the first assessment of High Arctic organic deposits using a high-resolution radiocarbon approach. Together with marine, glacial and lake records, peat archives of terrestrial change contribute to a clearer picture of polar region sensitivity over the last several thousand years.
PP51A-1480
Correlating the Pleistocene Sediment Stratigraphy Across the Arctic Ocean
An extensive sediment coring program was carried out during the Healy-Oden Trans-Arctic Expedition in 2005 (HOTRAX) from USCGC Healy. In total, 29 piston cores, on average 12 m long, were retrieved along a transect from the Alaskan margin, across the Arctic Ocean, to the Yermak Plateau off Svalbard. One of the purposes for the expedition was to establish the Pleistocene sediment stratigraphy for the Arctic Ocean and to resolve the issue of determining sedimentation rates in the central Arctic. Here, we present an attempt to correlate the cores along the HOTRAX transect in order to set a base for the chronostratigraphy. The cores taken from the Mendeleev Ridge and the Alpha Ridge can readily be correlated using gamma density and magnetic susceptibility measurements from the onboard Multi Sensor Core Logger as well as grain size measurements. The stratigraphic ties between the Alpha Ridge cores and the Mendeleev Ridge cores north of 80°N are detailed with many similar features. The most useful feature is an interval of five peaks in the magnetic susceptibility record. However, a correlation between the Mendeleev Ridge cores located further to the south and closer to the shelf edge was less straightforward, possibly indicating that depositional processes here are affected by other factors than in the central Arctic Ocean. Bridging the Amerasian and Eurasian Basin stratigraphies through the cores retrieved from the Lomonosov Ridge proved to be far less straightforward. None of the prominent physical property features that occur in the Mendeleev Ridge and Alpha Ridge cores are recognized in the Lomonosov Ridge stratigraphy. This may imply that the Lomonosov Ridge sediments predominantly originated from a different source area during the Pleistocene than the Alpha and Mendeleev Ridge sediments. Applying this as a working hypothesis, we focus on linking the cores within the Eurasian Basin for further correlation. However, the presence of alternating dark and light brown layers in all cores seem to indicate that the climatic signal should be recorded in all of them. Although no correlation across the entire Arctic Ocean has been achieved, the present results suggest that accurate core-to-core correlations are possible over large areas in the Amerasian Basin and that the depositional environment in the central Amerasian Basin has not varied significantly.
PP51A-1481
Itrax XRF-core scanner data provide new evidence for a mega event in the Arctic Ocean in cores from the YMER-80, ARCTIC OCEAN-96 and LOMROG-07 expeditions
During the Swedish icebreaker expeditions YMER-80, ARCTIC-96 and LOMROG-07 numerous piston and gravity cores were collected in the central Arctic Ocean and in the Fram Strait. These cores have been investigated using an Itrax X-ray fluorescence (XRF) Core Scanner at Stockholm University's core processing lab. The core scanner produces elemental profiles at high resolution for a wide range of elements. This work presents the first results from the XRF core scanning with a focus on elucidating a conspicuous thick, gray, and relatively homogeneous sediment unit that is present in most of the cores. The color, and physical properties of this unit makes it a significant break in the stratigraphy, which otherwise in the central Arctic Ocean cores is characterized by light yellowish brow clay with darker brown cycles. The XRF-signature of the gray unit consists of an anomaly of Ti, Fe, Ca and a redox-minimum of Mn. Out of the 31 investigated cores from these three expeditions, 24 contain the gray unit in the upper 2 m. These 24 cores are representative for the stratigraphy of the Eurasian side of the Lomonosov Ridge as well as the Gakkel Ridge, the Morris Jesup Rise and the Fram Strait. Comparing with the present Arctic Ocean circulation setting, the area where the gray layer occurs is characterized by the Transpolar Drift. Previously established age models for the central Arctic Ocean cores suggest that the gray layer was deposited during Marine Isotope Stage 4 (MIS 4). However, this age assignment must be considered uncertain as no chronological tie points exist directly in, above or below the gray layer. Radiographic images produced on two cores holding the gray layer shows a homogeneous, IRD-rich layer with no trace of bioturbation and with a very sharp base boundary, compared to a mottled well bioturbated material with an escape trace just beneath the gray layer. The sedimentological characteristics of this gray layer together with redox conditions, the escape trace and the sharp base boundary suggest a rapid deposition under oxygen free conditions. We suggest tentatively that the gray layer could be linked to the outburst of the Middle-Weichselian large ice-dammed lake in Western Siberia, and a following partial break up of the Eurasian ice sheet.
PP51A-1482
Cyclical variations in the ventilation of the central Arctic Ocean: evidence from XRF- scanning and X-radiographic studies of sedimentary structures
Cyclic variations in sediment color, Mn-concentrations, bioturbation intensity, and microfossil content observed in Pleistocene piston and gravity cores from the central Arctic Ocean have been attributed primarily to variations in deep water ventilation of the basin. During interglacial periods when ventilation presumably was strong Mn precipitated into conspicuous layers. These cyclical variations in ventilation where apparently in part driven by variations in sea level, which drastically altered the configuration of the basin on glacial- interglacial time scales. Here we present the first detailed X-ray radiograph study of late Pleistocene variations in biogenic structures from the deep Arctic Ocean. X-radiograph studies of variation in both intensity and type of bioturbation can deliver crucial information about the environmental conditions prevailing during the different phases, especially in interval where other proxies have been diagenetically altered. In particular, the radiographic images of the sediment can tell us whether the variations in bioturbation are coeval with the deposition of the Mn-rich layers, and consequently separate which Mn-layers are diagenetic in origin.
PP51A-1483
Radiocarbon Calibration of a High Resolution Core From the Central Arctic Ocean
The big challenge in calibrating radiocarbon dates to calendar years for Arctic Ocean deep sea sediments is to estimate the marine reservoir age of the water masses. Most sediment cores from the central Arctic Ocean have a low resolution and the preserved record for the last 25 ka is in the order of 10-20 cm. Therefore, most AMS 14C dating results are presented either uncalibrated or corrected. The used reservoir values often vary between 400 and 550 years, close to the global mean ocean reservoir age, since all available regional reservoir differences (ΔR) are from coastal areas around the Arctic Ocean. Our study presents 14C ages and calibration attempts with different modelled reservoir ages from a high resolution record of Holocene and Late Glacial sediments from the Lomonosov Ridge. During the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX) an area of the central Lomonosov Ridge, between about 88°15'- 89°N and 140°-180°E, was cored where a >1000 m deep depression characterizes the ridge morphology. Calcareous nannofossils (Fornaciari and Backman in prep.) and foraminifera analyzed in the upper 70 cm of core HLY0503-18TC show a sequence of the last ~130 ka. The chronology has been established through the nannofossil record in the lower 30 cm (Fornaciari and Backman in prep.) and 14C dating in the upper 40 cm. The data indicate very high accumulation rates during the Late Glacial of ~10 cm/ka, and times of extremely low to no accumulation during the Last Glacial Maximum, MIS 4 and parts of MIS 5. In addition, 14C dating on benthic and planktonic foraminifera from the same depth in the sediment core reveals age differences between surface and deep water masses. The age difference of such benthic-planktonic pairs shows a succession from ~1200 year older bottom waters in the Late Glacial to ~250 year in the late Holocene. This indicates circulation and/or ventilation changes through the last deglaciation and Holocene, which we hopefully will be able to date in greater detail with better model estimates of temporal changes in marine reservoir ages.
PP51A-1484
Radiocarbon Chronology Using Sedimentary Archaeal Tetraether Lipids in the Western Arctic Ocean
Recent drastic decrease of sea ice in the Arctic Ocean gives us the chance to collect the sediment core by non-icebreaker ship, which will induce the progress in understanding the Arctic environment under past climate change. However, it is not easy to establish more accurate age model of sediment cores because carbonate fossil such as planktonic foraminifera is very limited in the Arctic. In the glacial time, foraminifera is almost barren. Thus, so far high resolution records from the Arctic region is very sparse. We investigated sedimentary archaeal lipids as the material for chronology. Archaeal glycerol dibiphytanyl glycerol tetraether lipids (GDGTs) are derived from marine sources and have been used for reconstruction of paleo sea surface temperatures (TEX86). The sediment cores were retrieved from 2006 and 2008 Arctic expeditions by R/V Mirai. We will discuss radiocarbon data for the GDGTs, bulk-organic carbon, and foraminifera from the shelf to slope sediments in the western Arctic Ocean.
PP51A-1485
Development a Novel Method to Isolate Fatty Acids for Compound-specific Radiocarbon Dating to Reconstruct West Antarctic Ice Sheet Melting History
Previous reports suggested that radiocarbon dating of solvent-extractable, short-chain (C14, C16, and C18) fatty acids isolated from sediments are useful for reconstructing chronologies of Antarctic margin sediments. Compound-specific radiocarbon dating is potentially applicable as a chronological tool in the Arctic Ocean as well as in the other areas of Southern Ocean where the limitations of existing chronological tool have hindered the progress of palaeoceanographic studies. However, this approach requires technical progresses on the purification of target compounds from complex organic matrices since the methodology is also laborious and time-consuming. We present a novel method to isolate / purify these fatty acids using high- performance liquid chromatography / evaporative light scattering detector system (HPLC / ELSD). This new method is a key for compound-specific radiocarbon dating to become a mainstream of chronological tool in Antarctic margin and other high-latitude ocean sediments.
PP51A-1486
Timing of the last deglaciation in Skarvsnes, Lutzow-Holm Bay, East Antarctica
Quaternary climate is characterized by marked changes in global ice volume variations over glacial - interglacial cycles. Past changes in the global ice volume can be deduced from sea-level studies yet the contributions from various ice sheets for those changes have to be derived from observations near the ice sheets regions. Understanding of melting histories for ice sheets is critical to examine the sensitivities of ice sheets for climate changes and in particular for currently existing ice sheets. Future sea-level rise is anticipated due to ongoing global warming, caused by melting of both/either Greenland and/or Antarctic ice sheets. However, little is known past fluctuations of the ice volume of Antarctica because of difficulties in obtaining data, such as lack of datable materials, radiocarbon reservoir ages, and severe environments in the Southern Ocean. Cosmogenic radionuclide (CRN) dating offers a valuable alternative, allowing estimation of the direct exposure history of rocks once covered by the glaciers. The aim of this study is to reconstruct of East Antarctic Ice Sheet fluctuations using the CRN dating method, and to discuss the relation between ice sheet fluctuations and global sea-level changes. The concentration of in situ produced CRNs (Be-10, half-life = 1.50 Myr; and Al-26, half-life = 0.70 Myr) in quartz provides the cumulative exposure time of the rock. Also, the ratio of two CRNs (e.g. Al-26/Be-10) provides rock burial histories. Samples were obtained from the Skarvsnes ice-free area of the Lutzow-Holm Bay, East Antarctica. We collected 15 gneiss samples from 11 sites, consisting of 10 bedrock samples and other 5 erratic samples. The current findings are : (1) The timing of the last deglaciation of the Skarvsnes area was ca. 11 - 5 ka, (2) Melting of the East Antarctic Ice Sheet did not significantly contributed to rapid sea-level changes either 19 ka Mwp (Yokoyama et al., 2000) or Mwp 1a (Fairbanks, 1989; Bard, 1990). (3) The sea-level rise and/or sea-surface temperature rises are the cause of the East Antarctic Ice Sheet retreat in this region during the last deglaciation. (4) The East Antarctic Ice Sheet retreated at least once before the last deglacial period.
PP51A-1487
Pleistocene to Holocene Glaciomarine Environments in the Prydz Bay Region and its Implications for East Antarctic Ice Sheet Dynamics and Antarctic Bottom Water Production
The Lambert Graben-Amery Ice Shelf system is one of the world's largest outlet glaciers, draining about 20% of the East Antarctic Ice Sheet. It is an important feature for the global water budget and for the production of dense Antarctic Bottom Water, which contributes to the global Thermohaline Circulation. On the basis of environmental proxy data, inferred from sedimentological, mineralogical, and geochemical studies, the response of the glacial drainage system to climate changes in the past is investigated. Sediment cores from a depth transect down the continental slope off MacRobertson Land cover the time-span of the last one million years, revealed from palaeomagnetic data. At least three lithofacies units can be distinguished and related to different conditions of the depositional environment: (1) a massive sediment facies with a high content of sand and gravel, and a heavy-mineral assemblage dominated by hornblende, points to strong input of ice- rafted material, advantaged by open-water conditions and prolonged iceberg calving in Prydz Bay; (2) a lithofacies characterized by sand- and silt stringers in combination with conspicuous presence of sediment clasts, indicating sediment reworking and bulldozing over the shelf edge, and sediment dispersal to the deep by turbidity currents during times of increased ice-sheet mobility; (3) a clayey-silty laminite facies that captivates through a low amount of ice-rafted debris, suggesting stable glacial conditions and the activity of contourite currents. The longterm trend reveals the dominance of the massive sediment facies between 1000 and 650 ka and since 100 ka, while the interval in between is mostly characterized by the laminite facies. Apparently, downcore changes in lithofacies are hard to correlate with shortterm glacial-interglacial climate stages. Sediment cores from the Prydz Bay shelf and the MacRobertson shelf document the Holocene environmental history. Grain-size data of a sediment core recovered from MacRobertson shelf marks the onset of deglaciation at around 11.0 ka BP with enhanced bottom water circulation. The end of deglaciation appeared at around 8.8 ka BP and is associated with a drop in the supply of ice-rafted debris and increasing biogenic opal concentrations which then remain fairly constant through the Holocene with a short interruption 4.4 ka ago.
PP51A-1488
Effects of Earth Surface Albedo on Orbital Forcing in Quaternary Glacial Cycles
The saw-tooth pattern of fluctuation shown in climate proxy data such as those from Vostok ice core analysis has been a great mystery in the study of Earth's natural climate change. We believe that Earth's orbital cycles (Milankovitch cycles) set the pace for the climate progression. However, the albedo associated with sea surface, land surface and ice exerts a significant effect on the insolation received by the climate system which acts like a stack of heat capacitors. The middle heat capacitor (MHC), (i.e., the upper ocean) is stratified and thus the forcing to the climate system could be better represented by the global integral of sea- land and albedo-modulated insolation (SLAMI). The time series of SLAMI can easily explain the phase lead/lag between orbital cycle and climate variation. The peaks also successfully match climate records during the interglacial period. It also shows the fluctuation associated to the Glacial Termination (GT) is triggered by a mechanism that is explosively driven by the discharge of MHC. The saw-tooth pattern is formed with the composition of SLAMI and the MHC discharge.