Provenance Of Ice-rafted Debris Research Articles

Biomarker Fingerprint of Debris Flow Deposits as a Paleoproxy for IRD Sources in the Last Glacial North Atlantic

AbstractInvestigating the spatiotemporal dynamics of iceberg discharges during the last glacial period constitutes a major challenge for paleoclimate research. In recent decades, many ice‐rafted debris (IRD) provenance studies, mostly based on the comparison of the inorganic signature of IRD‐rich layers and surrounding continental bedrock, have differentiated main subareas of individual ice sheets as iceberg sources and gauged their dynamic interplay. Diagnosis of specific source ice streams has nonetheless remained limited. Here we propose a new IRD provenance methodology to refine the identification of iceberg sources. It relies on the organic geochemical characterization of glacigenic debris flow (GDF) deposits to obtain the biomarker fingerprint of IRD sources. To test its potential, we analyze the composition of n‐alkanes and chlorophyll‐derived pigments in sediments deposited within six major North Atlantic GDF depocenters fed by ice streams draining the surrounding ice sheets. The biomarker fingerprint of GDF deposits appears to (1) be consistent with a common origin of IRD and GDF deposits through erosion of outcrops and transport by ice streams, (2) differ significantly from that of ambient hemipelagic sediments, (3) be specific and unique to each GDF depocenter, making it possible to distinguish the corresponding specific ice streams, (4) be imprinted in IRD‐bearing marine sediments, and (5) have remained homogeneous enough through the last glacial to be used as a proxy for IRD sources. The biomarker fingerprint of GDF deposits thus shows strong potential to track the specific source ice streams that delivered IRD to the last glacial North Atlantic.

Trace elements and cathodoluminescence of detrital quartz in Arctic marine sediments – a new ice-rafted debris provenance proxy

Abstract. The records of ice-rafted debris (IRD) provenance in the North Atlantic–Barents Sea allow the reconstruction of the spatial and temporal changes of ice-flow drainage patterns during glacial and deglacial periods. In this study a new approach to characterization of the provenance of detrital quartz grains in the fraction > 500 μm of marine sediments offshore of Spitsbergen is introduced, utilizing scanning electron microscope backscattered electron and cathodoluminescence (CL) imaging, combined with laser ablation inductively coupled plasma mass spectrometry. Based on their micro-inclusions, CL and trace element characteristics, the investigated IRD grains can be classified into five distinct populations. Three of the populations are indicative of potential IRD provenance provinces in the Storfjord area including Barentsøya and Edgeøya. The results imply that under modern (interglacial) conditions IRD deposition along the western Spitsbergen margin is mainly governed by the East Spitsbergen Current controlling the ice-drift pattern. The presence of detrital quartz from local provinces, however, indicates that variations in IRD supply from western Spitsbergen may be quantified as well. In this pilot study it is demonstrated that this new approach applied on Arctic continental margin sediments bears a considerable potential for the definition of the sources of IRD and thus of spatial/temporal changes in ice-flow drainage patterns during glacial/interglacial cycles.

An alternative suggestion for the Pliocene onset of major northern hemisphere glaciation based on the geochemical provenance of North Atlantic Ocean ice-rafted debris

The onset of abundant ice-rafted debris (IRD) deposition in the Nordic Seas and subpolar North Atlantic Ocean 2.72 millions of years ago (Ma) is thought to record the Pliocene onset of major northern hemisphere glaciation (NHG) due to a synchronous advance of North American Laurentide, Scandinavian and Greenland ice-sheets to their marine calving margins during marine isotope stage (MIS) G6. Numerous marine and terrestrial records from the Nordic Seas region indicate that extensive ice sheets on Greenland and Scandinavia increased IRD inputs to these seas from 2.72 Ma. The timing of ice-sheet expansion on North America as tracked by IRD deposition in the subpolar North Atlantic Ocean, however, is less clear because both Europe and North America are potential sources for icebergs in this region. Moreover, cosmogenic-dating of terrestrial tills on North America indicate that the Laurentide Ice Sheet did not extend to ∼39°N until 2.4 ± 0.14 Ma, at least 180 ka after the onset of major IRD deposition at 2.72 Ma. To address this problem, we present the first detailed analysis of the geochemical provenance of individual sand-sized IRD deposited in the subpolar North Atlantic Ocean between MIS G6 and 100 (∼2.72–2.52 Ma). IRD provenance is assessed using laser ablation lead (Pb) isotope analyses of single ice-rafted (>150 μm) feldspar grains. To track when an ice-rafting setting consistent with major NHG first occurred in the North Atlantic Ocean during the Pliocene intensification of NHG (iNHG), we investigate when the Pb-isotope composition (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) of feldspars deposited at DSDP Site 611 first resembles that determined for IRD deposited at this site during MIS 100 (2.52 Ma), the oldest glacial for which there exists convincing evidence for widespread glaciation of North America. Whilst Quaternary-magnitude IRD fluxes exist at Site 611 during glacials from 2.72 Ma, we find that the provenance of this IRD is not constant. Instead, we find that the Pb-isotope composition of IRD at our study site is not consistent with major NHG until MIS G2 (2.64 Ma). We hypothesise that IRD deposition in the North Atlantic Ocean prior to MIS G2 was dominated by iceberg calving from Greenland and Scandinavia. We further suggest that the grounding line of continental ice on Northeast America may not have extended onto the continental shelf and calved significant numbers of icebergs to the North Atlantic Ocean during glacials until 2.64 Ma.

Provenance of North Atlantic ice-rafted debris during the last deglaciation—A new application of U-Pb rutile and zircon geochronology

Understanding the provenance of ice-rafted debris (IRD) provides a means to link the behavior of individual ice sheets to proxy records of climate change. Here we present a new approach to determining IRD provenance using U-Pb geochronology of detrital minerals rutile and zircon. We characterize potential source regions from Scotland using detrital rutile from modern fluvial systems, and demonstrate that their unimodal rutile U-Pb ages reflect the timing of the last amphibolite facies metamorphism of the source rocks, imparting a distinctive source signature. Contrasts between these spectra and the bimodal IRD (ca. 470 Ma and ca. 1800–2000 Ma) rutile age signatures rule out Scotland as the sole source and suggest a Laurentian contribution; IRD zircon ages further support this view. U-Pb mineral dating has the potential to provide new insight on IRD provenance, because it allows linkage between IRD and individual source terranes based on their differing magmatic and tectonothermal histories. The occurrence of Laurentian-sourced IRD proximal to Scotland demonstrates widespread and rapid dispersal of debris across the subpolar North Atlantic during the Older Dryas cold oscillation, and implicates the Atlantic meridional overturning circulation as a control. This highlights the sensitivity of some IRD records to rapid climate change during the last deglaciation and supports the interpretation of Heinrich events as time-parallel marker horizons.

Flux and provenance of ice-rafted debris in the earliest Pleistocene sub-polar North Atlantic Ocean comparable to the last glacial maximum

Relatively little is known in detail about the locations of the early Pleistocene ice-sheets responsible for ice-rafted debris (IRD) inputs to the sub-polar North Atlantic Ocean during intensification of northern hemisphere glaciation (iNHG). To shed new light on this problem, we present the first combined in-depth analysis of IRD flux and geochemical provenance of individual sand-sized IRD deposited in the sub-polar North Atlantic Ocean during the earliest large amplitude Pleistocene glacial, marine isotope stage (MIS) 100 (∼2.52Ma), arguably the key glacial during iNHG. IRD provenance is assessed using laser ablation lead (Pb) isotope analyses of single feldspar grains. We find that the Pb-isotope composition (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) of individual ice-rafted (>150μm) feldspars deposited at DSDP Site 611A, ODP Site 981 and IODP Site U1308 during MIS 100 records a shift from predominantly Archaean-aged circum-North Atlantic Ocean continental sources during early glacial ice-rafting events to dominantly Palaeozoic and Proterozoic-aged sources during full glacial conditions. The distribution of feldspars in Pb–Pb space for full glacial MIS 100 more closely resembles that documented for feldspars deposited at the centre of the last glacial IRD belt (at IODP/DSDP Site U1308/609) during ambient (non-Heinrich-event) ice-rafting episodes of MIS 2 (∼23.8ka) than that documented for MIS 5d (∼106ka). Comparison of our early Pleistocene and last glacial cycle datasets suggests that MIS 100 was characterised by abundant iceberg calving from large ice-sheets on multiple continents in the high northern latitudes (not just on Greenland).

Characterizing the sediment provenance of East Antarctica's weak underbelly: The Aurora and Wilkes sub‐glacial basins

The Wilkes and Aurora basins are large, low‐lying sub‐glacial basins that may cause areas of weakness in the overlying East Antarctic ice sheet. Previous work based on ice‐rafted debris (IRD) provenance analyses found evidence for massive iceberg discharges from these areas during the late Miocene and Pliocene. Here we characterize the sediments shed from the inferred areas of weakness along this margin (94°E to 165°E) by measuring40Ar/39Ar ages of 292 individual detrital hornblende grains from eight marine sediment core locations off East Antarctica and Nd isotopic compositions of the bulk fine fraction from the same sediments. We further expand the toolbox for Antarctic IRD provenance analyses by exploring the application of 40Ar/39Ar ages of detrital biotites; biotite as an IRD tracer eliminates lithological biases imposed by only analyzing hornblendes and allows for characterization of samples with low IRD concentrations. Our data quadruples the number of detrital 40Ar/39Ar ages from this margin of East Antarctica and leads to the following conclusions: (1) Four main sectors between the Ross Sea and Prydz Bay, separated by ice drainage divides, are distinguishable based upon the combination of 40Ar/39Ar ages of detrital hornblende and biotite grains and the εNd of the bulk fine fraction; (2) 40Ar/39Ar biotite ages can be used as a robust provenance tracer for this part of East Antarctica; and (3) sediments shed from the coastal areas of the Aurora and Wilkes sub‐glacial basins can be clearly distinguished from one another based upon their isotopic fingerprints.

Magnetic signature of European margin sediments: Provenance of ice‐rafted debris and the climatic response of the British ice sheet during Marine Isotope Stages 2 and 3

Mineral magnetic measurements are used to distinguish ice‐rafted debris (IRD) sources and climate cycles spanning Marine Isotope Stage (MIS) 3 and MIS2 in core MD95–2006, from the Barra Fan, NE Atlantic. Distinct magnetic properties are displayed by IRD from the Laurentide ice sheet (LIS) (high susceptibility (χ), low isothermal remanent magnetization (IRM), low coercivity and the Verwey transition), the British ice sheet (BIS) (high χ, high IRM, medium coercivity and suppressed Verwey transition) and the ambient background sediment (low χ and low IRM). A magnetic unmixing model quantifies proportions of the IRD sources during Greenland Stadial (GS) 16 to GS3 (57.3 to 22.6 ka B.P.) spanning Heinrich Event (H) 5 to H2. The magnetic model suggests LIS IRD is only dominant within an interval during GS9, assigned to H4. Prior to H4 low proportions of BIS IRD suggest the BIS was not able to deliver significant amounts of IRD into the marine system. Following H4, proportions of BIS IRD during stadials increase, suggesting growth of the BIS during the latter stages of MIS3, with further expansion of the BIS during MIS2. LIS IRD within H2 is masked by BIS IRD input. Climatically driven anhysteretic remanent magnetizations reflect the short Dansgaard‐Oeschger cycles between H5 and H4, while the proportions of hard magnetic minerals reflect the longer‐term Bond cycles.

Introduction to special section on Cenozoic Paleoceanography of the Central Arctic Ocean

[1] In late summer 2004, the Integrated Ocean Drilling Program (IODP) conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling: the Arctic Coring Expedition (ACEX) [Backman et al., 2006; Moran et al., 2006a]. This technically challenging expedition [Moran et al., 2006b] to the Lomonosov Ridge near 88 N recovered the first long-term Cenozoic sediment record from the Arctic Ocean–extending previous records from 1.5 Ma to an unprecedented 56 Ma. Glimpses of the breadth of this transformation were seen during the ACEX cruise when the massulae from freshwater ferns (Azolla) were found in 49 Ma old sediments [Brinkhuis et al., 2006] and the presence of Apectodinium augustum confirmed that the Paleocene-Eocene thermal maximum (PETM) (55 Ma) was unexpectedly recovered [Sluijs et al., 2006]. [2] Soon after the expedition, when the cores were opened and analyzed, ice-rafted debris was found in surprisingly old (46 Ma) sediments [Moran et al., 2006a]. These middle Eocene sediments are characterized also by their high organic carbon content [Stein et al., 2006]. The exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people. Analyses were extended to include studies that revealed surprisingly high Arctic Ocean surface water temperatures [Sluijs et al., 2006] and an amplified hydrological system [Pagani et al., 2006] during the PETM. Initial analyses revealed an extensive hiatus encompassing about 26 million years that occurred below a short interval showing starkly alternating black and white layers that is now dubbed the ‘‘zebra’’ interval; thus the time interval from the late early Miocene (18 Ma) to the middle middle Eocene (44 Ma) is missing. Although the hiatus is a lost window in time for the Arctic paleoclimate record, it spawned other studies that integrated the regional tectonic history with ACEX results revealing a major oceanographic reorganization at 17.5 Ma–ventilation of the Arctic Ocean to the North Atlantic through the Fram Strait [Jakobsson et al., 2007]. In terms of ventilation and water mass history, Neogene neodymium isotope data reveal that Arctic Intermediate Waters originate from brine formation on Eurasian shelf areas between 15 and 2 Ma, and during glacial periods throughout Pleistocene times [Haley et al., 2008a]. They conclude that this mode of Arctic circulation differs markedly from today’s situation, showing relatively high contributions of North Atlantic Intermediate Water and minor input from brine formation. [3] In this special section, the transformation continues. Results from the large ACEX scientific ‘‘family’’ include: a robust age model; detailed analyses of the middle Eocene that document a unique brackish water environment; sea ice and iceberg history reconstructions as well as the provenance of ice-rafted debris from the Eocene to present; evolution of depositional environments; times of isolation and connection to the global ocean; geochemical analyses of the organic carbon-rich sediments; and unique applications of high-resolution proxies and cyclostratigraphy. Highlights from this special section are presented here.

Ice shelf history from petrographic and foraminiferal evidence, Northeast Antarctic Peninsula

A detailed record of late Pleistocene deglaciation followed by mid-Holocene ice shelf breakup and late Holocene re-growth is contained in continental shelf sediments in the northern Larsen area, northeast Antarctic Peninsula. The zero age of core tops is confirmed by new and published 210Pb profiles, and 70 accelerator mass spectrometer (AMS) 14C dates on bulk organic carbon define sedimentation rates of 7.6–92 cm/ka. The varied geology in the local ice drainage basins facilitates the use of ice-rafted debris (IRD) provenance in determining the presence or absence of ice shelves. All inshore cores contain an interval of non-local IRD in the post-glacial section, demonstrating widespread ice shelf breakup in the mid-Holocene. Both breakup and re-growth may have taken centuries and there are no widespread debris layers associated with breakup. Cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied IRD provenance throughout the Holocene, suggesting the maximum ice shelf limit may date only from the Little Ice Age. Benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes. Nevertheless we discern a deglaciation signal in Prince Gustav Channel of a calcareous spike in predominantly agglutinated assemblages, and this is repeated at the time of mid-Holocene ice shelf breakup. The inferred mid-Holocene warm period occurred later in the northern Larsen area than on the west coast of the Antarctic Peninsula.

Mid- to Late Pleistocene Ice Drift in the Western Arctic Ocean: Evidence for a Different Circulation in the Past

The provenance of ice-rafted debris (IRD) in four Arctic sediment cores implies that icebergs from the northwestern Laurentide ice sheets drifted across the western Arctic Ocean along the 180°–0° meridian toward Fram Strait during mid- to late Pleistocene deglaciations within the last 700,000 years. This iceberg drift was different from the present-day Beaufort Gyre circulation and resembled a dislocated transpolar drift (TPD). Sea ice mainly followed the iceberg trajectories but also frequently drifted from the Russian shelves eastward into the Amerasian Basin.