Abundance Of Ice-rafted Debris Research Articles

Late Miocene to Early Pliocene paleoceanographic evolution of the Central South Pacific: A deep-sea benthic foraminiferal perspective

The bottom water conditions in the Central South Pacific (CSP) and associated changes in the Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW) under warmer-than-present conditions need to be better understood. These water masses transfer their properties to the major ocean basins. We analyzed Late Miocene to Early Pliocene (5.6–3.6 Ma) marine sediment core sections from the CSP for benthic foraminifera, ice rafted debris (IRD), Ostracoda, planktic foraminifera Orbulina universa abundance, and organic geochemical proxies to assess the bottom water characteristics under warmer-than-present day conditions. A significant increase in IRD abundance between 5.3 and 4.9 Ma marks the Early Pliocene warm phase. The benthic foraminiferal assemblages indicate shifts in bottom water conditions over time in the CSP region. Between 5.6 and 5.3 Ma, predominantly oxygenated bottom water with moderate organic matter flux prevailed. This shifted to suboxic conditions with increased organic matter flux from 5.3 to 4.9 Ma. Subsequently, between 4.9 and 4.4 Ma, bottom water conditions alternated frequently between oxic and suboxic states. Enhanced bottom water formation and inflow of LCDW and AABW in the CSP during 4.4–4.0 Ma promoted oxygenated conditions, accompanied by low organic export flux. However, sluggish bottom water circulation from 4.0 to 3.6 Ma reverted to suboxic conditions, associated with increased carbon burial. Notably, productivity peaked intermittently between 5.3 and 3.6 Ma, as indicated by the occurrence of suboxic species assemblages and increase in the abundance of Orbulina universa, benthic microfauna (ostracods), and other paleoproductivity indicators.

Changing sediment supply during glacial-interglacial intervals in the North Atlantic revealed by particle size characterization and environmental magnetism

The Pliocene-Pleistocene transition is characterized by an abundance of Ice-Rafted Debris (IRD) in the North Atlantic basin. One of the regions affected by IRD during this period is the Gardar Drift, where the DSDP Leg 94 Hole 611A is located. This region received sediments from different sources during the glacial and interglacial intervals (e.g., Iceland and Greenland). We analyzed grain size and particle-size specific magnetic properties of sediments for their provenance characterization between ~2.64 and 2.52 Ma. Our results show that major proportion of bulk sediments during both glacial and interglacial periods were made up of basaltic-rich Icelandic sediments, whereas only during more intense glacial periods (Marine Isotope Stages 100 and 104), a small proportion of non-basaltic sand compositions were identified, possibly sourced from Greenland and other non-basaltic provenances. The non-basaltic sand fractions during the intense glacial periods were likely supplied as IRDs. In addition, a new level of coarse lithics (38 pcs. of >1 mm) composed of different rocks types (e.g., basalt, granite, granodiorite etc.) were identified in DSDP 611A Hole during the end of glacial MIS 104. The coarse lithic fragments showed distinctive magnetic properties than rest of the particle sizes and were classified as Iceberg-Rafted Debris (IBRD). Our results show that higher sand percentage was found during the intense glacial episodes, and their magnetic grain size analysis could help in distinguishing their provenance. We elaborate that particle size specific magnetic measurements of sand fractions could help in rapidly characterizing the glacial episodes in the subpolar North Atlantic.

A ~240 ka record of Ice Sheet and Ocean interactions on the Snorri Drift, SW of Iceland

Core MD99-2323 was extracted from the Snorri Drift at a water depth of 1062 m, just south of the Denmark Strait, and ~120 km from the Last Glacial Maximum (LGM) margins of the Iceland and East Greenland Ice Sheets. The core chronology (~7.5 to 240 cal ka) is derived from radiocarbon dates, marker tephra, paleomagnetic excursion, and correlation with North Atlantic δ18O records on Neogloboquadrina pachyderma (δ18ONp). Sedimentation averaged ~7.5 cm/kyr. Records of proxy flow speed, ice rafted debris (IRD) and oxygen isotopes show that many IRD abundance peaks represent winnowing of the fine fraction by faster flows rather than pulses of increased IRD flux. The overall pattern of flow speed does not resemble the classic fast interglacial/slow glacial pattern seen in records of Nordic Sea overflow, rather the current record is suggested to be partly controlled by the production of brine-driven gravity flows from adjacent ice fronts, especially during cold periods. On a smaller scale the usual glacial/slow – interglacial/fast pattern appears to be the case during ~5 kyr oscillations during Marine Isotope Stage (MIS) 6 where periodic low flow speed is matched by high values of planktonic oxygen isotope ratios. Eight peaks in quartz wt% reflect increased contributions from glacial erosion of Precambrian and Caledonian bedrock from E and NE Greenland; peaks in dolomite may reflect glacial-marine transport from the Laurentide Ice Sheet. Cross wavelet analysis of the δ18ONp versus sortable silt and quartz records indicate significant precession and obliquity periodicities, but with little temporal correlations due to leads and lags in responses.

Evidence of Southern Ocean influence into the far Northwest Pacific (Northern Emperor Rise) since the Bølling–Allerød warming

The role of the Southern Ocean in releasing CO 2 (sequestered in the global ocean during the Last Glacial Maximum) into the atmosphere during deglaciation is an important topic for investigation of Earth's climate. Changes in global deep water circulation associated with upwelling of Circumpolar Deep Water (CDW) around Antarctica may have played a part in the CO 2 release, but remain poorly studied. The potential response of the Pacific Ocean, including the North Pacific, to upwelling of CDW with its vast reservoir of CO 2 remains unresolved. Here we combine productivity proxies, oxygen and carbon isotope values in benthic and planktic foraminifera, data on the occurrence and abundance of ice-rafted debris, and benthic foraminiferal species composition in three sediment cores with published data for three cores from the Northern Emperor Rise for the Last Glacial Maximum, deglaciation and Holocene in order to elucidate the North Pacific role in CO 2 redistribution in the past. Age models of the cores are based on radiocarbon data calibrated by 14 C atmospheric plateau tuning. The calcium carbonate content in all cores increased abruptly around 14.5 ka, indicating an influx of relatively young water enriched in carbonate ion, oxygen and nutrients, and sourced in the Southern Oceans. A decrease in the extent of sea ice at the NER area during early deglaciation is reflected in sharp increases in the productivity of siliceous phytoplankton near the onset of Bølling/Allerød warming, possibly facilitated by the influx of Southern Ocean-sourced nutrient-rich waters. • Stable isotope, lithological and micropaleontological proxies of 6 cores from the Western Subarctic Gyre (WSG) were studied. • Age models of cores over the last 25kyr were modified by radiocarbon data calibrated by 14C atmospheric plateau tuning. • Multiple lines of evidences support abrupt flushing of Southern Ocean origin water into the deep WSG since 14.5 ± 0.2 ka.

Minimal Holocene retreat of large tidewater glaciers in K\xf8ge Bugt, southeast Greenland

Køge Bugt, in southeast Greenland, hosts three of the largest glaciers of the Greenland Ice Sheet; these have been major contributors to ice loss in the last two decades. Despite its importance, the Holocene history of this area has not been investigated. We present a 9100 year sediment core record of glaciological and oceanographic changes from analysis of foraminiferal assemblages, the abundance of ice-rafted debris, and sortable silt grain size data. Results show that ice-rafted debris accumulated constantly throughout the core; this demonstrates that glaciers in Køge Bugt remained in tidewater settings throughout the last 9100 years. This observation constrains maximum Holocene glacier retreat here to less than 6 km from present-day positions. Retreat was minimal despite oceanic and climatic conditions during the early-Holocene that were at least as warm as the present-day. The limited Holocene retreat of glaciers in Køge Bugt was controlled by the subglacial topography of the area; the steeply sloping bed allowed glaciers here to stabilise during retreat. These findings underscore the need to account for individual glacier geometry when predicting future behaviour. We anticipate that glaciers in Køge Bugt will remain in stable configurations in the near-future, despite the predicted continuation of atmospheric and oceanic warming.

Evidence for regional cooling, frontal advances, and East Greenland Ice Sheet changes during the demise of the last interglacial

Abstract High-resolution lithic and sea surface climate records are used to portray the progression of North Atlantic climate, hydrography, and Greenland Ice Sheet (GIS) activity through the peak of Marine Isotope Stage (MIS) 5e into the last glacial inception. We use Eirik Drift sediment core MD03-2664 (57°26.34′N, 48°36.35′W), recovered south of Greenland, strategically located to monitor fluctuations in GIS extent and iceberg calving events. Our results show that a significant amount of ice-rafted debris (IRD) was present during the early MIS 5e, until gradually tapering off by 122 kyr BP due to a diminishing GIS. Sea surface temperatures (SSTs) in the northern subpolar gyre reached peak values early in MIS 5e coinciding with peak insolation. Regional cooling leading to the demise of the last interglacial started prior to the end of the MIS 5e benthic δ18O plateau, at approximately 119 kyr BP, as summer insolation waned. This gradual cooling trend is interrupted by an abrupt and brief cooling episode at ∼117 kyr BP. Increased IRD abundance during the 117 kyr BP cooling event suggests that regional ice sheet growth occurred prior to the end of the MIS 5e benthic δ18O plateau, and the major glacial inception. SSTs south of Greenland followed a two-step cooling during the glacial inception similar to the pattern observed across much of the North Atlantic and Europe. Benthic δ18O increases in parallel, suggesting that this two-step cooling is linked to a two-phased intensification of Northern Hemisphere glaciation.

A shape and compositional analysis of ice-rafted debris in cores from IODP Expedition 323 in the Bering Sea

Sediment cores recovered during IODP Expedition 323 in the Bering Sea, northern Pacific, contained numerous ice-rafted debris (IRD) clasts up to 85mm in length. The physical properties (including roundness and sphericity) of 136 clasts from the working half of the cores, a subsample of the total clast number, were analysed and their composition determined using standard petrographic techniques. After removal of pumice and possible fall-in derived material from the clast population, a total of 86 clasts from the original collection were considered to be IRD. While roundness and sphericity vary greatly in the clast population, the IRD are predominately discoid in shape with oblate/prolate indices typically between −5 and 5. There are four time periods over the approximately 4.5Ma sample interval, 0.36–0.67Ma, 0.82–1.06Ma 1.54–1.77Ma and >3.28Ma, where there are no IRD in the sample set for sites of the Bering slope, suggesting that these times may have been ice-free. Most clasts show some rounding and are likely to have spent time on beaches with wave action. Wave action on beaches suggests periods of no ice or only seasonal sea-ice. The low roundness values of other clasts, however, suggest they underwent little working and, therefore, the presence of glaciers or more permanent sea-ice at times in those locations. The abundance of rounded and unfaceted clasts as IRD suggests a lack of large ice sheets in the area during cool periods. Clast composition of the IRD is divided into four broad groups, basalt and andesite, granite and metamorphic, sedimentary, and felsic volcanic. The granite and metamorphic and more mature sedimentary lithologies are most likely derived from the Alaskan continental margin, while the extrusive igneous clasts could be derived from a variety of volcanic sources surrounding the Bering Sea, both emergent now or emergent at times of lower sea level. There is only a poor correlation with IRD abundance and marine isotope stages (MIS) for the time period <1Ma. Abundant IRD occurs in MIS 3 and can be correlated with MIS back to 400kyr but not to older ages. This suggests that the abundance of IRD >2mm transported by sea-ice may not be a good indicator of past climate conditions.

Fluctuations in the late Quaternary East Asian winter monsoon recorded in sediment records of surface water cooling in the northern Japan Sea

AbstractThe East Asian monsoon climate system involves interactions between land and ocean and is composed of summer and winter monsoons. Cooling of surface water by the East Asian winter monsoon (EAWM) promotes the formation of sea ice and deep water in the northern Japan Sea. Modern observations suggest close relationships between intensification of the EAWM and both sea ice formation and sea‐surface temperature (SST) decrease in the northeastern Japan Sea. Records of ice‐rafted debris (IRD) and alkenone‐based SST in the northeastern Japan Sea are examined to clarify the temporal variability of the EAWM and its controlling factors. Close relationships with oxygen isotope records of Chinese stalagmites and Northern Hemisphere summer insolation are observed in the records of IRD occurrence and SST during Marine Isotope Stages (MIS) 3–5. The co‐occurrence of maxima in the abundance of IRD and minima in SST in the northeastern Japan Sea indicates that the intensity of the EAWM was enhanced during periods of low summer insolation and high oxygen isotope ratios in Chinese stalagmites. Decoupling between the IRD and SST records during MIS 2 and MIS 6 might be the result of differences in surface water conditions caused by low sea levels and the resultant closure of the Tsushima Strait. During MIS 3 and 4, some small but clear maxima in IRD and minima in SST occurred at relatively low summer insolation periods. Some of these peaks co‐occur with North Atlantic Heinrich events, suggesting a possible climate linkage between the North Atlantic and the Asian monsoon. The presence of finer fluctuations in the occurrence of IRD than in summer insolation suggests finer millennial–centurial timescale fluctuations in the intensity of the EAWM. Furthermore, some IRD peaks occurred during periods of high insolation, such as 39, 86, 103, 128, 145, and 153 ka. Some of these IRD peaks correlate with minima in reconstructed SST and maxima in oxygen isotope ratios of Chinese stalagmites. This result suggests that extremely cold winters occur even during periods of enhanced East Asian summer monsoon intensity, and indicates that solar insolation is not the only factor that controls variations in the intensity of the EAWM at millennial–centurial timescales. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Influence of Late Quaternary depositional environments on the structure of nannofossil assemblages in the Titanic area (northwestern Atlantic)

The nannofosssil assemblages have been analyzed in five cores taken from the Titanic area of the northwestern Atlantic (∼41°–42° N, ∼47°–50° W, water depths >3500 m) during cruises 41 and 43 of the R/V Akademik Mstislav Keldysh in 1998 and 2000. They correlate the host sediments with the upper Pleistocene-Holocene Emiliania huxleyi zone. The changes in the structure of the nannofossil assemblages and the lithological characteristics such as the content of biogenic CaCO3, the abundance of ice-rafted debris, and the grain-size composition were used for the high-resolution stratigraphy of sections with defining marine isotopic stages 1–3 of the last 24 kyr. A characteristic feature of the nannofossil assemblages from this area is their enrichment with the cold-resistant species Coccolthus pelagicus during the warm climatic stages and the lack of allochthonous coccolitophorid remains.

Plio-Pleistocene trends in ice rafted debris on the Lomonosov Ridge

Although more than 700 sediment cores exist from the Arctic Ocean, the Plio-Pleistocene evolution of the basin and its marginal seas remains virtually unknown. This is largely due the shallow penetration of most of these records, and difficulties associated with deriving chronologies for the recovered material. The Integrated Ocean Drilling Program's (IODP) Expedition 302 (Arctic Coring Expedition, ACEX) recovered 197 m of Neogene/Quaternary sediment from the circumpolar regions of the Lomonosov Ridge. As detailed analyses of this material emerge, research is beginning to formulate a long-term picture of paleoceanographic changes in the central Arctic Ocean. This paper reviews the ACEX Plio-Pleistocene age model, identifies uncertainties, and addresses ways in which these may be eliminated. Within the established stratigraphic framework, a notable reduction in the abundance of ice rafted debris (IRD) occurs in the early part of the Pleistocene and persists until Marine Isotope Stage 6 (MIS 6). Therefore, while global oceanographic proxies indicate the gradual growth of terrestrial ice-sheets during this time, IRD delivery to the central Arctic Ocean remained comparatively low and stable. Within the resolution of existing data, the Pleistocene reduction in IRD is synchronous with predicted changes in both the inflow of North Atlantic and Pacific waters, which in modern times are known to exert a strong influence on sea ice stability.

Comparison of ice-rafted debris and physical properties in ODP Site 1094 (South Atlantic) with the Vostok ice core over the last four climatic cycles

Visual counts of ice-rafted debris (IRD), foraminifera, and radiolaria were made for ∼1500 samples in Site 1094 spanning the last four climatic cycles (marine isotope stages 1–11). Most, but not all, of the IRD variability is captured by whole-core physical properties including magnetic susceptibility and γ-ray attenuation bulk density. Glacial periods are marked by high IRD abundance and millennial-scale variability, which may reflect instability of ice shelves in the Weddell Sea region. Each interglacial period exhibits low IRD and high foraminiferal abundance during the early part of the interglacial, indicating relatively warm sea-surface temperatures and reduced influence of sea ice. IRD increases and foraminiferal abundances decrease during the latter part of each interglacial, indicating a return to more glacial-like conditions. Glacial terminations I and V are each characterized by a step-wise reduction in ice-rafting punctuated by a brief pulse in IRD delivery and reversal in δ 18O. The coarse fraction of the sediment is dominated by ash and radiolaria, and the relative abundance of these components is remarkably similar to the concentration of Na + in Vostok. Each of these variables is believed to be controlled mainly by sea-ice cover, thereby providing a means for sediment–ice core correlation.

Separation of primary ice-rafted debris from lag deposits, utilizing manganese micronodule accumulation rates in abyssal sediments of the Southern Ocean

Changes in the abundance of ice-rafted debris in abyssal sediments of the Southern Ocean have been interpreted as evidence of variations in Antarctic glacial activity. When accompanied by a simultaneous increase in Mn micronodules, however, it is proposed that ice-rafted debris maxima may represent residual lag deposits, created during a period of reduced sedimentation rate caused by selective removal of the finer or lighter fraction by high-velocity bottom currents. An empirical relationship between ice-rafted debris and Mn micronodules in the southeast Pacific Ocean has been used to suppress the lag component in the total ice-rafted debris signal in order to isolate the ice-rafted debris caused by increased iceberg supply associated with increases in glacial activity in Antarctica. The spatial distribution of the mean accumulation rate of ice-rafted debris during the past 690,000 yr is complicated by local bottom-scouring activity, which causes erratic latitudinal variations of total ice-rafted debris accumulation rates. When the residual portion of ice-rafted debris is removed, a coherent latitudinal decrease of the mean accumulation rate of debris is revealed. The average northern limit of debris during the past 690,000 yr is not different from present conditions. A sharp maximum in debris accumulation occurs in the vicinity of the present Antarctic convergence, suggesting that the factors governing iceberg supply and melting rate have not changed appreciably during the period involved. Six periods of increases in Mn micronodule production are defined at intervals of 100,000 to 110,000 ± 20,000 yr. The linear correlation coefficient between ice-rafted debris and Mn micronodules during the past 690,000 yr defines two areas of intense winnowing, separated by the East Pacific Rise. The southernmost zone corresponds to an area independently described as one of high bottom-current activity. Our results indicate that the intensity of bottom-current winnowing on the north flank of the East Pacific Rise may be as great as in the southern zone. This could mean that the Eltanin Fracture Zone serves as a conduit for high-velocity Antarctic Bottom Water flowing onto the northern flank of the East Pacific Rise.