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Quaternary sediment in the Labrador Sea was derived from many proglacial sources in Greenland and eastern Canada. Understanding the spatial and temporal changes in sediment provenance provides information on ice extent and sediment dispersal patterns. Variations in mineral composition of sediment from late Quaternary cores has been determined by a whole pattern of quantitative X-ray diffraction procedure. Mineral facies were extracted statistically by a supervised analysis of 90 samples from bedrock and ice-rafted clasts, which were then used to predict the most probable mineral facies in 1443 marine sediment samples. We used a non-parametric Classification Decision Tree (CDT) to validate that decision. Only 26% of the samples were misclassified in the CDT. The six facies identified consisted of four facies reflecting differences in the composition of Canadian and Greenland Precambrian igneous and metamorphic bedrock, a set of samples dominated by high weight percentages of calcite and dolomite (detrital carbonate (DC) and Hudson Strait Heinrich (HS-H) events), and a “shale” facies. We isolated 284 sediments from the HS-H DC facies and determined that they could be divided into four categories based on differences in their mineral proportions. These categories vary geographically, based on non-carbonate sediment supply during these events from Greenland, the Canadian Shield, the Appalachians, and the outer continental shelf. In the Holocene of the Labrador Sea, dolomite is derived from Baffin Bay and abundance of calcite is influenced by both biogenic productivity and dissolution.

Glacial marine sediment deposition varies both spatially and temporally, but nearly all studies evaluate down-core (∼ time) variations in sediment variables with little consideration for across core variability, or even the consistency of a data set over distance scales of 1 to 1000 m. Grain size and quantitative X-ray diffraction (qXRD) methods require only ≤ 1 g of sediment and thus analyses assume that the identification of coarse sand (i.e., ice-rafted debris) and sediment mineral composition are representative of the depth intervals. This assumption was tested for grain size and mineral weight % on core MD99-2317, off East Greenland. Samples were taken from two sections of the core that had contrasting coarse-sand content. A total of fourteen samples were taken consisting of seven (vertical) and two (horizontal) samples, with five replicates per sample for qXRD analyses and ∼ 10 to 20 replicates for grain size. They had an average dry weight of 10.5 ± 0.5 g and are compared with two previous sets of sediment samples that averaged 54.1 ± 18.9 g and 20.77 ± 5.8 g dry weight. The results indicated some significant differences between the pairs of samples for grain-size parameters (mean sortable silt, and median grain size) but little difference in the estimates of mineral weight percentages. Out of 84 paired mineral and grain-size comparisons only 17 were significantly different at p = < 0.05 in the post-hoc Scheffe test, all of which were linked to grain-size attributes.

Most extant small ice caps mantling low-relief Arctic Canada landscapes remained cold-based throughout the late Holocene, preserving in situ bryophytes killed as ice expanded across vegetated landscapes. As Arctic summers warmed after 1900 CE, ice caps receded, exposing entombed vegetation. The calibrated radiocarbon ages of dead moss collected near ice-cap margins (kill-dates) define when ice advanced across the site, killing the moss, and remained over the site until the year of their collection. In an earlier study we reported 94 Last Millennium radiocarbon dates on in situ dead moss collected at the margins of two upland ice complexes on northern Baffin Island, Arctic Canada. Tight clustering of those ages indicated an abrupt onset of the Little Ice Age ~1240 CE, and further expansion ~1480 CE, coincident with episodes of major explosive volcanism. Here we test the confidence in kill dates as reliable predictors of expanding ice caps by re-sampling those previously sampled ice complexes 14 years later, after ~250 m of ice recession. The probability density functions (PDF) of the more recent series of ages matches PDFs of the earlier series, but with a larger fraction of early CE ages; post 2005 CE ice recession has exposed relict ice caps that grew during earlier Common Era advances, and were preserved beneath later ice-cap growth. We compare 107 kill dates from the two ice complexes with 79 kill dates from 62 other ice caps within 250 km of the two densely sampled ice complexes. The PDF of kill dates from the 62 other ice caps cluster in the same time windows as those from the two ice complexes alone, with the PDF of all 186 kill dates documenting episodes of widespread ice expansion restricted almost exclusively to 250–450 CE, 850–1000 CE and a dense early Little Ice Age cluster with peaks at ~1240 and ~1480 CE. Ice continued to expand after 1480 CE, reaching maximum dimensions ~1880 CE, still visible as zones of limited vegetation cover in remotely sensed imagery. Intervals of widespread ice-cap expansion coincide with persistent decreases in mean summer surface air temperature for the region in a Community Earth System Modeling (CESM) fully coupled Common Era simulation, suggesting primary forcing of the observed snowline lowerings were both modest declines in summer insolation, and cooling resulting from explosive volcanism, most likely intensified by positive feedbacks from sea-ice expansion and reduced northward heat transport by the oceans. The clusters of ice cap expansion defined by moss kill-dates are mirrored in an annually resolved Common Era record of ice-cap dimensions in Iceland, suggesting this is a circum-North-Atlantic-Arctic climate signal for the Common Era. During the coldest century of the Common Era, 1780–1880 CE, ice caps mantled > 11,000 km2 of north-central Baffin Island, whereas < 100 km2 is glaciated at present. That state approached conditions expected during the inception phase of an ice age, and was only reversed after 1880 CE by anthropogenic alterations of the planetary energy balance.

We evaluate the linkages between lithofacies and mineral composition of late Quaternary sediments along the Baffin Slope for cores 2013029 64, 74, and 77. Four major lithofacies were identified: diamicton (L1), laminated red-brown mud (L2), tan carbonate mud (L3), and brown bioturbated mud (L4). In addition, gold-brown mud (L2a) beds were identified within red-brown mud throughout the Baffin margin and a thin, locally distributed light gray mud (L2b), also identified within red-brown mud, was localized to the Home Bay region. A classification decision tree (CDT) correctly predicted ∼ 87% of the lithofacies based on five binary choices based on the estimated weight %s of (in order): quartz, kaolinite, plagioclase, iron oxides, and smectites. The detrital tan carbonate (DC) minerals, calcite and dolomite, did not appear in the chosen CDT solution although this lithofacies is easily recognized in cores because of its tan color and the facies is well predicted in the CDT. The addition of grain size did not substantially improve the prediction of the lithofacies although it did change the % importance of the minerals in the CDT.

The goal of the paper is to ascertain whether there are significant regional variations in sediment mineral composition that might be used to elucidate ice sheet histories. The weight percentages of nonclay and clay minerals were determined by quantitative X-ray diffraction. Cluster analysis, an unsupervised learning approach, is used to group sediment mineralogy of 263 seafloor/core top samples between ∼80°N and 62°N. The optimum number of clusters, based on 30 indexes, was three for the weight percentage data but varied with data transformations. Maps of the distribution of the three mineral clusters or facies indicate a significant difference in weight percentages between samples from the West Greenland and Baffin Island shelves. However, several indexes support a larger number of clusters and similar analyses of the spatial distribution and defining minerals of nine mineral facies indicated a strong association with the original three clusters and with broad geographic designations (i.e., West Greenland shelf, Baffin Island fiords, etc). Classification Decision Tree analysis indicates that this difference is primarily controlled by the percentages of plagioclase feldspars versus alkali feldspars.

There are climatically important ocean flow systems in high latitudes, for example the East and West Greenland and Labrador Currents and Nordic Sea overflows in the North, and Antarctic Circumpolar Current in the South, for which it would be useful to know history of flow strength. Most of the sediment records under these flows contain evidence of supply from glacial sources, which has led to the supposition that fine sediment records, which in other settings provide evidence of vigour of flow from the sortable silt proxy, are fatally contaminated by unsorted glacial silt. It is suggested here that if the fine fraction ( 50%) because the two are not related. End member (EM) decomposition of several records yields variable results in terms of the relationship between EM ratios and grainsize parameters. Although such an approach can generate fine sediment parameters it does not provide a basis for deciding whether or not a record is acceptably current sorted and thus contains a valid flow speed proxy. Our proposed discrimination between current-sorted and unsorted fine fractions is applicable to all fine grained deposits, not only high-latitude deposits with coarse IRD. Examples from East Greenland, Faroe Bank Channel, Gardar Drift show mainly well sorted signatures. Amounts of coarse IRD range up to 60% with only those >50% having a consistent impact on sortable silt mean size. With the exception of a Southern Ocean site on the Antarctic continental rise where half the record is poorly sorted, the silt mean data are sufficiently well sorted to provide credible flow speed histories. This bodes well for the extraction of such histories from climatically important high-latitude flows such as the East Greenland Current.

Publisher's version (útgefin grein), Strong similarities in Holocene climate reconstructions derived from multiple proxies (BSi, TOC – total organic carbon, δ13C, C∕N, MS – magnetic susceptibility, δ15N) preserved in sediments from both glacial and non-glacial lakes across Iceland indicate a relatively warm early to mid Holocene from 10 to 6 ka, overprinted with cold excursions presumably related to meltwater impact on North Atlantic circulation until 7.9 ka. Sediment in lakes from glacial catchments indicates their catchments were ice-free during this interval. Statistical treatment of the high-resolution multi-proxy paleoclimate lake records shows that despite great variability in catchment characteristics, the sediment records document more or less synchronous abrupt, cold departures as opposed to the smoothly decreasing trend in Northern Hemisphere summer insolation. Although all lake records document a decline in summer temperature through the Holocene consistent with the regular decline in summer insolation, the onset of significant summer cooling occurs ∼5 ka at high-elevation interior sites but is variably later at sites closer to the coast, suggesting that proximity to the sea may modulate the impact from decreasing summer insolation. The timing of glacier inception during the mid Holocene is determined by the descent of the equilibrium line altitude (ELA), which is dominated by the evolution of summer temperature as summer insolation declined as well as changes in sea surface temperature for coastal glacial systems. The glacial response to the ELA decline is also highly dependent on the local topography. The initial ∼5 ka nucleation of Langjökull in the highlands of Iceland defines the onset of neoglaciation in Iceland. Subsequently, a stepwise expansion of both Langjökull and northeast Vatnajökull occurred between 4.5 and 4.0 ka, with a second abrupt expansion ∼3 ka. Due to its coastal setting and lower topographic threshold, the initial appearance of Drangajökull in the NW of Iceland was delayed until ∼2.3 ka. All lake records reflect abrupt summer temperature and catchment disturbance at ∼4.5 ka, statistically indistinguishable from the global 4.2 ka event, and a second widespread abrupt disturbance at 3.0 ka, similar to the stepwise expansion of Langjökull and northeast Vatnajökull. Both are intervals characterized by large explosive volcanism and tephra distribution in Iceland resulting in intensified local soil erosion. The most widespread increase in glacier advance, landscape instability, and soil erosion occurred shortly after 2 ka, likely due to a complex combination of increased impact from volcanic tephra deposition, cooling climate, and increased sea ice off the coast of Iceland. All lake records indicate a strong decline in temperature ∼1.5 ka, which culminated during the Little Ice Age (1250–1850 CE) when the glaciers reached their maximum Holocene dimensions., This work was supported primarily by the Icelandic Center for Research through grants awarded to Áslaug Geirsdóttir and Gifford H. Miller (no. 130775051 and Grant of Excellence no. 141573052) and several grants awarded to Áslaug Geirsdóttir from the UI Research Fund. We thank Sædís Ólafsdóttir, Celene Blair, Sydney Gunnarson, Sarah Crump, Thorsteinn Jónsson, and Sveinbjörn Steinthorsson, who all contributed to this work by taking part in field work, laboratory analyses, and/or discussion. Thorough and constructive reviews from two anonymous reviewers have substantially improved the paper.

International audience; Radiocarbon dates and marine tephra suggest that the upper 10 m of core MD99-2274 off North Iceland extends from ∼0 to ∼65 ka BP. A multi-proxy sediment and biomarker study at a ∼0.5 ky resolution is used to derive a paleoclimate scenario for this area of the southwestern Nordic Seas, which during the Holocene had intermittent excursions of icebergs and a seasonal cover of drifting sea ice across the site. The sortable silt mean size (S̅S̅) suggests a bottom current (1000 m depth) flow speed maximum to minimum range of ∼8 cm/s during Marine Isotope Stages 2–3, but the data are unreliable for the Holocene. Slow-down in flow speeds may be associated with massive ice and water discharges linked to the Hudson Strait ice stream (H-events) and to melt of icebergs from Greenland in the Nordic seas where convection would have been suppressed. Five pulses of sediment with a distinct felsic component are associated with iceberg transport from E/NE Greenland. Sea ice, open water and sea surface temperature (SST) biomarker proxies (i.e. IP25, HBI III, brassicasterol and alkenones) all point towards near-perennial sea ice cover during MIS 3 and 2, rather than seasonal sea ice or open water conditions. Indeed, our biomarker and sediment data require that the seas north of Iceland experienced a nearly continuous cover of sea ice, together with icebergs calved from ice stream termini, which drifted southward. The cross-correlation of the quartz % records between MD99-2274 and the well-dated core PS2644 in Blosseville Basin indicates significant coherence in the records at a multi-millennial (∼8 ky) timescale. A transition to open ocean conditions is evident from the early Holocene onwards, albeit with the occurrence of some drift ice and icebergs.

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.

Calving events of Petermann Glacier, northwest Greenland, in 2010 and 2012 reduced the length of its ice tongue by c. 25 km, allowing exploration of newly uncovered seafloor during the Petermann 2015 Expedition. This article presents the results of foraminiferal analysis and environmental data from thirteen surface sediment samples in northern Nares Strait and Petermann Fjord, including beneath the modern ice tongue. This is the first study of living foraminifera beneath an arctic ice tongue and the first modern foraminiferal data from this area. Modern assemblages were studied to constrain species environmental preferences and to improve paleoenvironmental interpretations of foraminiferal assemblages. Sub–ice tongue assemblages differed greatly from those at all other sites, with very low faunal abundances and being dominated by agglutinated fauna, likely reflecting low food supply under the ice tongue. Fjord fauna were comprised of 80 percent or more calcareous species. Notably, Elphidium clavatum is absent beneath the ice tongue although it is dominant in the fjord. Increasing primary productivity associated with the transition to mobile sea ice, diminishing influence of the Petermann Glacier meltwater with distance from the grounding line, and increased influence of south-flowing currents in Nares Strait are the important controls on the faunal assemblages.

Biogeochemical proxy records from Icelandic lake sediment reflect large-scale shifts in North Atlantic Holocene climate and highlight the impact that North Atlantic Ocean- and atmospheric circulation has on Iceland’s local climate. Following Early Holocene warmth, millennial-scale cooling has been modulated by centennial-scale climate change, culminating in the transition to the Little Ice Age (ca. 1300-1900 CE). Although the long-term cooling trend is presumably driven by variations in Earth’s orbit and the concomitant decline in Northern Hemisphere summer insolation, the centennial-scale variability has been linked to variations in solar irradiance, the strength of the Atlantic Meridional Overturning Circulation, volcanism coupled with sea ice/ocean related feedbacks and internal modes of atmospheric variability. One manifestation of these regional climate changes on Iceland is the intensification of soil erosion, resulting in the degradation of its eco-systems and landscape. In recent millennia, persistent and severe soil erosion has also been linked to human impact on the environment following the settlement ~874 CE, rapid population growth and the poorly consolidated nature of tephra dominated soils. However, against the argument that the onset of severe soil erosion coincided with human settlement are composite landscape stability proxies extracted from the high-resolution, precisely-dated lake sediment cores. These data suggest event-dominated landscape instability and soil erosion began in the Middle to Late Holocene with an intensification of landscape instability around ~500 CE, several centuries before the acknowledged settlement of Iceland, after which soil erosion continue to increase. In order to statistically identify abrupt and persistent changes within our landscape stability proxy records, we performed an analysis that targets mean regime shifts in individual time series. The first clear regime shift occured around ~500 CE, with a second large shift ~1200 CE. In order to provide a causal explanation for these regime shifts, we looked to a new 2 ka fully coupled climate transient simulation using CESM1, with forcing data from PMIP4, including insolation, volcanic aerosols, land-cover, and GHG. The CESM results show a ~0.5°C reduction in summer temperature in the first millennium CE, consistent with increased landscape instability and soil erosion in Iceland. A second phase of persistent summer cooling in the model occurs after 1150 CE, with stronger cooling after 1450 CE, reaching a minimum shortly after 1850 CE, ~1°C lower than at the start of the experiment. Orbitally driven declines in summer insolation appear to be the dominant forcing early in the first millennium CE, with volcanism and solar irradiance reductions increasingly important after 500 CE and in the second millennium CE, but positive feedbacks from sea ice and the overturning circulation are necessary to explain the magnitude of peak LIA cooling when soil erosion is at its greatest in Iceland. Collectively, our initial results suggest that natural variations in regional climate and volcanism are likely responsible for soil erosion prior to human impact, with intensification of these processes following settlement particularly during the cooling associated with the Little Ice Age.

Quantitative X-ray diffraction (qXRD) mineralogy of bedrock, ice-rafted, and fluvial clasts, 239 seafloor samples (

Records from cores 2011031-059 and 2011031-062 (hereafter 59 and 62) have been used to reconstruct changes in the vigor of the Labrador Current in northern Flemish Pass during the last glacial cycle. Grain size proxies for current speed, planktonic foramiferal δ18O, X-ray diffraction analysis for dolomite and calcite, and abundance of ice-rafted detritus (IRD) have been determined. An age model back to Marine Isotope Stage (MIS) 5 is based on recognition of seven Heinrich events from total dolomite and calcite, correlated to the IODP U1302/3 record, and confirmed by O-isotope stratigraphy and radiocarbon dates. A straight-line relationship between mean size of sortable silt ( SS ¯ ) and percent of sortable silt (SS%) and the lack of relationship between SS ¯ and IRD (> 500 μm) indicate well-sorted sediments in cores 59 and 62, which can be used to reconstruct the paleocurrent intensity. Intensified current vigor occurred in MIS 5, 3 and 1, so that warmer periods show faster currents, probably through the Irminger Current component of the North Atlantic subpolar gyre. Low values of δ18O, SS% and SS ¯ correspond to H events, suggesting a slowdown in the Labrador Current, followed by a rapid return to strong circulation. In some cases current vigor recovery lagged slightly after the H events. Heinrich events with larger amounts of meltwater show higher current vigor. Correlation with deep-water current vigor records in the Iceland Basin show a broad correlation on a multi-millennial scale with Labrador Current variations. As our study is on a shallow sediment drift formed by the Labrador Current, one of the surface currents of the North Atlantic sub-polar gyre, it provides new evidence for a tight connection between surface current vigor fluctuation and the vigor of the deep thermohaline circulation.

We provide a test for recent arguments that the West Antarctic Ice Sheet (WAIS) is underlain by an extensive outcrop of volcanic rock (mainly basalt) by examining the non-clay and clay mineral composition of sediments collected in front of and under the Ross Ice Shelf. If the proposed large volume were present, then we posit that glacial erosion and transport would deliver sediments to the Ross Sea enriched in minerals diagnostic of alkaline basalt, namely olivine, pyroxene, and plagioclase, and no quartz. Using quantitative X-ray diffraction analysis, we determine the weight percent of minerals in West Antarctic alkaline basalt, dolerite, gneiss, and granite bedrock, and compare these with a suite of 49 surface and near-surface sediment samples from a 1400 km west to east transect across the Ross Sea. Fifty percent of the samples had quartz percentage values >25% and had very small wt percentages of diagnostic basalt minerals. A sediment unmixing algorithm, with basalt, dolerite, gneiss and granite bedrock, end members, showed that the sediment contained virtually no basalt, was dominated by granite compositions, but did show some samples with an admixture of material derived from the Ferrar dolerite, which crops out extensively in the Transantarctic Mountains. Indicators of possible late Cenozoic volcanic bedrock – pyroxene, forsterite, and smectite weight percentages – decrease from west to east across the Ross Sea opposite to the trend of the quartz weight percent. Our study provides no support for the presence of extensive basalt outcrop under the WAIS, hence indicates that any changes in ice stream stability will not be influenced by basal heat regime.

The dynamics of the Greenland Ice Sheet and drift of sea ice from the Arctic Ocean reaching Denmark Strait are poorly constrained. We present data on the provenance of Fe oxide detrital grains from two cores in the Denmark Strait area and compare the Fe grain source data with other environmental proxies in order to document the variations and potential periodicities in ice-rafted debris delivery during the Holocene. Based on their Fe grain geochemistry, the sediments can be traced to East Greenland sources and to more distal sites around the Arctic Basin. On the Holocene time scales of the two cores, sea ice biomarker (IP25) data, and quartz weight percent reveal positive associations with T°C and inverse associations with biogenic carbonate wt%. Trends in the data were obtained from Singular Spectrum Analysis (SSA), and residuals were tested for cyclicity. Trends on the environmental proxies explained between 15 and 90% of the variance. At both sites the primary Fe grain sources were from Greenl...

Marine sediment cores that span the last 50,000 years frequently show considerable variability in sediment and biogeochemical variables. In the North Atlantic, a series of massive iceberg and meltwater events (Heinrich events) were sourced from Hudson Strait and the Laurentide Ice Sheet with a periodicity of ~7.2 ky and had significant impacts on the Atlantic meridional overturning circulation and the global hydrological and biogeochemical cycles. Some marine proxies show higher frequency, abrupt events, that may match the Dansgaard-Oeschger (D-O) oscillations. Predictable millennial-scale periodicities and associated forcings have proved elusive, and an observed ~1.5 ky cycle may be linked to stochastic resonance. 01500/2014, 04326/2020 info:eu-repo/semantics/publishedVersion

Hemipelagic sediment on the upper continental slope is commonly transported from the adjacent continental shelf, but along-slope transport of sediment by thermohaline currents may be an important source of sediment. One such case is Flemish Cap, a promontory of the eastern Canadian continental shelf protected from direct continental sediment supply by the deep-water Flemish Pass. Pleistocene sediment drifts around Flemish Cap accumulated glacially derived sediment from the north, transported by the Labrador Current. This study determines the changing sources and controls on the accumulation of bioturbated hemipelagic sediment through the Holocene. From a set of >150 box cores in water depths of 600–1200 m, some 30 push cores, up to 55 cm long, were studied in detail for stratigraphic variation in grain size, bulk geochemistry (XRF) and detrital petrology (granule petrology and qXRD). Criteria were developed to identify trawling disturbance. Two Holocene stratigraphic units, A) almost lacking ice-rafted detritus and B) with some coarse IRD and higher detrital carbonate, correlate with similar units farther north on the Labrador Shelf and Slope. Sedimentation rates based on 26 radiocarbon dates were ~ 0.02–0.03 m/ka over much of the region below the 800 m isobath, locally reaching 0.1 m/ka in some sediment drifts, but as low as 0.01 m/ka on southeastern Flemish Cap. Where sedimentation rate was >0.03 m/ka, the record of flow vigor from the sortable silt proxy since 6 ka shows three different zones of Labrador Current flow with different timing of changes in flow vigor. The mid to early Holocene record shows that the meltwater-driven inner Labrador Current extended across the entire study area. Where sedimentation rates are lower, periods of sediment bypassing are inferred and the sortable silt record varies little. Correlation with external drivers is hampered by century-scale core resolution and sparse dating control. The distinctive abundance of dolomite rock flour in hemipelagic sediments around Flemish Cap indicates important supply from Baffin Bay icebergs during the entire Holocene, diluted prior to 6 ka by sediment from Hudson Strait and some Labrador ice streams. Baffin Bay icebergs melt preferentially in the southern Labrador Sea, dropping their load, with the fine grained component transported to the south by the Labrador Current. Similar partitioning of coarse- from fine-grained components of IRD may take place on other high-latitude outer continental margins.

5584 Background: Activity of durvalumab in patients with deficient mismatch repair (dMMR) advanced endometrial carcinoma (EC) was confirmed in the PHAEDRA trial (ANZGOG 1601). This study investigated the association between immune biomarkers and clinical outcomes in PHAEDRA. Methods: Formalin-fixed paraffin embedded sections immunohistochemically stained for PD-L1 using the Ventana platform, were with matched H&E slides scored independently by two pathologists according to the Ventana PD-L1 (SP263) algorithm for urothelial carcinoma (UC). Immune biomarkers assessed were PD-L1 staining of tumor cells (TCP) and immune cells (IC), and presence of tumor-associated immune cells (ICP). Results: Sixty-seven of the 71 patients had sufficient tumor for PD-L1 testing. AUC were 0.667, 0.726 and 0.644 for TCP, ICP and IC, respectively for predicting tumor response. Optimal cutpoints were TCP≥1%, ICP≥10% and IC≥35%. ICP≥10% achieved the highest sensitivity (53%) and specificity (82%) of the individual cutpoints. The optimal cutpoint algorithm was able to identify patients who would not respond, (sensitivity 88%, negative predictive value 92%), but had low specificity (48%) and positive predictive value (37%). Differences in PFS were found using ICP≥10% (logrank p = 0.01), compared to TCP (p = 0.25), IC (p = 0.48) and the UC algorithm (p = 0.08) (Figure 1). PFS was shorter in patients with pMMR than dMMR after adjusting for ICP (HR 2.99, 95%CI: 1.61-5.57, p < 0.001). Adjustment for MMR reduced the prognostic significance of ICP≥10% for PFS (HR 0.59, 95% CI: 0.28-1.23, p = 0.16). For OS, differences were seen for the UC algorithm (p = 0.02), but not ICP (p = 0.07), TCP (p = 0.18) or IC (p = 0.23). Similarly to PFS, adjustment for MMR reduced the prognostic significance of the UC algorithm for OS (HR: 0.53, 95% CI: 0.25-1.12, p = 0.10). Conclusions: In this exploratory analysis, ICP was more closely associated with tumor response and PFS than TCP or IC. ICP alone was better than the UC algorithm for predicting PFS. The optimum cutpoint algorithm was promising for identifying non-responders, but requires external validation. Clinical trial information: ACTRN12617000106336.

North Iceland represents a climatically sensitive region, in part, due to its location at the confluence of southward flowing and drift ice-laden polar waters from the Arctic Ocean delivered by the East Greenland Current, and the relatively warm and saline Irminger Current, a northerly flowing branch of the North Atlantic Current. Despite its pivotal location, there is a paucity of high resolution and long-term sea ice records for the region, with some disparities in certain previous investigations. Here, the identification of the biomarker IP 25 as a reliable proxy for drift ice for North Iceland has been confirmed by measuring its abundance in surface sediments from the region and comparison of outcomes with documentary records of sea ice and other proxy data. By analysing IP 25 in a well-dated marine sediment core from the North Icelandic Shelf (NIS) (MD99-2269), we also provide a high resolution (ca. 25 yr) record of drift sea ice for the region and complement this with a lower resolution record (ca. 100 yr) obtained from a second core site, located further east (JR51-GC35). Statistical treatment of equi-spaced time series reveals strong linear correlations between IP 25 and a further drift ice proxy (quartz) in each core. Thus, linear regression analysis between both proxies gave correlation coefficients (R 2 ) of 0.74 and 0.66 for MD99-2269 (25 yr) and JR51-GC35 (100 yr), respectively. Further, the individual proxies were well correlated between the two cores, with R = 0.91 and 0.77 for IP 25 and quartz, respectively. The IP 25 -based sea ice record for MD99-2269, combined with other new biomarker and foraminifera data, and previously published proxy data for primary productivity and sea surface temperature, suggest that the paleoceanographic evolution for the NIS over the last 8 ka can be classified into three main intervals. The early mid Holocene (ca 8–6.2 cal ka BP) was characterized by relatively low or absent drift ice, low primary productivity and relatively high SSTs. During the mid-Holocene (ca 6.2–3.3 cal ka BP), drift ice increased concomitant with decreasing SSTs, although primary productivity was somewhat enhanced during this interval. IP 25 first reached its mean value for the entire record at ca 5 cal ka BP, before increasing, continuously, ca 4.3 cal ka BP, broadly in line with the onset of Neoglaciation as seen in some other proxy records. Further increases in drift ice were evident during the late Holocene (ca 3.3 cal ka BP to present), culminating in maximum sea ice during the Little Ice Age. In addition, the IP 25 record from MD99-2269 shows some positive regime shifts from the general trend, especially at ca 3.8, 2.7, 1.5, 0.7 and 0.4 cal ka BP, that have analogs in some other paleoceanographic reconstructions influenced by the East Greenland Current. The abrupt increases in IP 25 at ca 1.5 and 0.7 cal ka BP are coincident with rapid cooling identified previously in an Icelandic lacustrine temperature record, suggesting significant coupling between the marine and terrestrial systems. The contribution of sea ice to the broader climate system is further evidenced through the identification of statistically significant periodicities (ca 1000 yr and ca 200–230 yr) in the drift ice proxy data that have counterparts in previous studies concerning atmospheric and oceanic variability and solar forcing mechanisms.

To evaluate whether proxies that record surface, near-surface, and bottom water conditions from the North Iceland shelf have similar trends and periodicities, we examine Holocene century-scale paleoceanographic records from core MD99-2269. This core site lies close to the boundary between Atlantic and Arctic/Polar waters, and in an area frequently influenced by drift ice. The proxies are stable δ13C and δ18O values on planktonic and benthic foraminifera, alkenone-based sea-surface temperatures (SST°C), and foraminiferal Mg/Ca SST°C and bottom water temperature (BWT°C) estimates. These data were converted to equi-spaced 60-year time-series; significant trends were extracted using Singular Spectrum Analysis, which accounted for between 50% and 70% of the variance. In order to evaluate within-site ocean climate variability, a comparison between these data and previously published proxies from MD99-2269 was carried out on a standardized data set of 14 proxies covering the interval 400–9200 cal. yr BP. Principal component (PC) analysis indicated that the first two PC axes accounted for 57% of the variability with high loadings primarily defining ‘nutrient’ and ‘temperature’ proxies. Fuzzy k-mean clustering of the 14 climate proxies indicated major environmental changes at ~6350 and ~3450 cal. yr BP, which define local early-, middle-, and late-Holocene climatic shifts. Our results indicate that the major control on the combined proxy signal is the Holocene decrease in June insolation, but regional changes in such factors as sea-ice extent and salinity are required to explain the threefold division of the Holocene.

In order to document changes in Holocene glacier extent and activity in NE Greenland (~73° N) we study marine sediment records that extend from the fjords (PS2631 and PS2640), across the shelf (PS2623 and PS2641), to the Greenland Sea (JM07-174GC). The primary bedrock geology of the source areas is the Caledonian sediment outcrop, including Devonian red beds, plus early Neoproterozoic gneisses and early Tertiary volcanics. We examine the variations in colour (CIE*), grain size, and bulk mineralogy (from X-ray diffraction of the 2 mm) and IRD-grain-size spectra are rare in the last 9–10 cal. ka BP and, in contrast with areas farther south (~68° N), there is no distinct IRD signal at the onset of neoglaciation. Our paper demonstrates the importance of the quantitative analysis of sediment properties in clarifying source to sink changes in glacial marine environments.

To investigate the mechanisms behind Holocene regional climate trends from north of 58°N in the North Atlantic-Fennoscandian region Principal Component Analysis (PCA) was performed and a temperature anomaly stack produced from 81 proxy derived summer temperature time series from 74 sites. The PC results show distinctly different trends for near-surface versus surface temperatures, demonstrating the importance of handling these separately. The first PC of weighted sea surface summer temperature time series and continental time series explains 45 ± 8% of the variance, where the uncertainty is the standard deviation of the distribution of variance explained across the 1000 age-uncertain ensemble members. PC1 has a relatively uniform expression over the whole region, closely following the summer insolation at 65°N. The second PC explains 22 ± 4% of the variance and shows a non-uniform expression, with loadings in opposite directions in the northern and southeastern parts of the region. Comparing the PC time series with model runs and with the timing of the demise of the Laurentide Ice Sheet (LIS), suggest that this pattern reflects both topographic and albedo effects of the LIS as well as release of meltwater into the North Atlantic and Arctic Oceans. Comparing the stack of gridded records with published global stacks reveals an unusual Holocene temperature development in the North Atlantic-Fennoscandian region most likely resulting from the location relative to the decaying LIS.

John Hollin died on 3 October 2016 after a long and courageous battle with multiple sclerosis complicated at the end by cancer. John was born in 1930 in Derby, England, and lived there until he was...

Biogeochemical proxy records from Icelandic lake sediment track large-scale shifts in North Atlantic Holocene climate and highlight the impact that North Atlantic Ocean- and atmospheric circulation has on Iceland’s climate and environment. Following Early Holocene warmth, centennial-scale climate change is superimposed on millennial-scale cooling, culminating in the transition to the Little Ice Age (∼1300–1900 CE). Although the long-term cooling trend is presumably driven by variations in Earth’s orbit and the concomitant decline in Northern Hemisphere (NH) summer insolation, the centennial-scale variability has been linked to the strength of the Atlantic Meridional Overturning Circulation (AMOC), volcanism coupled with sea ice/ocean related feedbacks, internal modes of atmospheric variability, and plausibly variations in solar irradiance. One manifestation of these regional climate changes on Iceland is the intensification of soil erosion, resulting in the degradation of ecosystems and landscape. In recent millennia, persistent and severe soil erosion has also been linked to human impact on the environment following the settlement ∼870 CE, rapid population growth, introduction of livestock and the poorly consolidated nature of tephra dominated soils. Lake proxy composite records suggest that although event-dominated landscape instability and soil erosion from the Early to Middle Holocene were likely triggered by large volcanic eruptions, the landscape was capable of recovering. However, a threshold was reached ∼5 ka BP, resulting in a state change whereby the Icelandic landscape could no longer fully recover from cold-events and/or tephra fall. Landscape sensitivity to climate further intensified at ∼1.5 ka BP as identified by regime shift analysis. Hence, widespread and irreversible soil erosion began several centuries before the acknowledged settlement of Iceland, with a second acceleration ∼1250 CE. A 2 ka fully coupled climate transient simulation using CESM1.1 shows a ∼0.5 °C reduction in summer temperature around Iceland in the first millennium CE, consistent with increased landscape instability and soil erosion in Iceland. A second phase of persistent summer cooling in the model occurs after 1150 CE, with stronger cooling after 1450 CE, reaching a maximum shortly after 1850 CE, ∼1 °C lower than at the start of the simulation. Our results suggest that natural variations in regional climate and volcanism are likely responsible for soil erosion prior to human impact, with intensification of these processes following settlement particularly during the cooling associated with the Little Ice Age. Given that the conclusions drawn in this review diverge from the standard paradigm of human-induced soil erosion history in Iceland, research should continue to focus on this complex question from multiple disciplines. In particular, a combination of emerging biogeochemical techniques (e.g. lipid biomarkers and ancient DNA) may be best poised to test and quantify the relative roles of natural environmental variables and human settlement in the history of soil erosion on Iceland.

The goal of this paper is to employ quantitative methods to: first, describe the spatial variations in the quantitative non-clay and clay mineral composition of seafloor (surface) sediments; secondly, use those data to describe the temporal variations in mineral compositions of nine cores that extend (variously) between the present-day and ~85 ka BP; and thirdly, describe regional variations in the transport of felsic- versus mafic-rich glacial marine sediments at four sites close to Denmark Strait. K-mean clusters of recent seafloor samples (n = 156) distinguished four mineral facies, which characterize a range of mafic to felsic compositions. These samples serve as a training set to identify the down-core mineral facies in eight cores (n = 1053); the degree of provenance mixing is measured by fuzzy clustering on an unsupervised cluster analysis. Classification Decision Trees validate the mineral facies (only 6% misclassified) and indicate that variations in the weight % of pyroxene are of primary importance in defining cluster membership. Mineral compositions identify two end member core sites JM07-174GC (Greenland Sea) and LO9-18 (Reykjanes Ridge), while the cores north and south of the Greenland-Faroes Ridge (cores PS2644, MD99-2274, -2280, and -2323) are a mixture of mafic-rich and felsic-rich mineral facies. Variations in magnetic susceptibility and quartz wt% exhibit coherent runs of values above or below their medians in three of the cores occurred, indicating that these cannot be ascribed to random variations (p

Strong similarities in Holocene climate reconstructions derived from multiple proxies (BSi, TOC, δ13C, C/N, MS, δ15N) preserved in sediments from both glacial and non-glacial lakes across Iceland indicate a relatively warm early-to-mid Holocene from 10 to 6 ka, overprinted with cold excursions presumably related to meltwater impact on North Atlantic circulation until 7.9 ka. Sediment in lakes from glacial catchments indicates their catchments were ice-free during this interval. Statistical treatment of the high-resolution multiproxy paleoclimate lake records shows that despite great variability in catchment characteristics, the records document more or less synchronous abrupt, cold departures as opposed to the smoothly decreasing trend in Northern Hemisphere summer insolation. Although all lake records document a decline in summer temperature through the Holocene consistent with the regular decline in summer insolation, the onset of significant summer cooling, occurs ~5 ka in high-elevation interior sites, but is variably later in sites closer to the coast, suggesting some combination of changing ocean currents and sea ice modulate the impact from decreasing summer insolation. The timing of glacier inception during the mid-Holocene is determined by the decent of the Equilibrium Line Altitude (ELA), which is dominated by the evolution of summer temperature as summer insolation declined as well as changes in sea surface temperature for glacial systems particularly in coastal settings. The glacial response to the ELA decline is also highly dependent on the local topography. The initial nucleation of Langjökull in the highlands of Iceland starting by ca 5 ka, was followed by a stepwise expansion of both Langjökull and northeast Vatnajökull between 4.5 and 4.0 ka, with a second abrupt expansion ca. 3 ka. However, the initial appearance of Drangajökull in the NW of Iceland was delayed until after 2.5 ka. All lake records reflect abrupt summer temperature and catchment disturbance at about 4.5 ka, statistically indistinguishable from the ~4.2 ka event with a second widespread abrupt disturbance centered on 3.0 ka. Both are intervals of large explosive volcanism on Iceland. The most widespread increase in glacier advance, landscape instability, and soil erosion occurred shortly after 2 ka, likely due to a complex combination of increased impact from volcanic activity, cooling climate, and increased sea ice off the coast of Iceland. All lake records indicate a strong decline in temperature ~1.5 ka, culminating during the Little Ice Age between 1300 and 1900 CE when most glaciers reached their maximum dimensions.

In the area of Denmark Strait (~66° N), the two modes of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) are expressed in changes of the northward flux of Atlantic water and the southward advection of polar water in the East Iceland current. Proxies from marine cores along an environmental gradient from extensive to little or no drift ice, capture low frequency variations over the last 2000 cal yr BP. Key proxies are the weight% of calcite, a measure of surface water stratification and nutrient supply, the weight% of quartz, a measure of drift ice transport, and grain size. Records from Nansen and Kangerlussuaq fjords show variable ice-rafted debris (IRD) records but have distinct mineralogy associated with differences in the fjord catchment bedrock. A comparison between cores on either side of the Denmark Strait (MD99-2322 and MD99-2269) show a remarkable millennial-scale similarity in the trends of the weight% of calcite with a trough reached during the Little Ice Age. However, the quartz records from these two sites are quite different. The calcite records from the Denmark Strait parallel the 2000 yr Arctic summer-temperature reconstructions; analysis of the detrended calcite and quartz data reveal significant multi-decadal–century periodicities superimposed on a major environmental shift occurring ca. 1450 AD.

Core HU2008029-12PC from the Disko trough mouth fan on the central West Greenland continental slope is used to test whether an ice shelf covered Baffin Bay during the Last Glacial Maximum (LGM) and at the onset of the deglaciation. We use benthic and planktic foraminiferal assemblages, stable isotope analysis of planktic forams, algal biomarkers, ice-rafted detritus (IRD), lithofacies characteristics defined from CT scans, and quantitative mineralogy to reconstruct paleoceanographic conditions, sediment processes and sediment provenance. The chronology is based on radiocarbon dates on planktic foraminifers using a ∆ R of 140 ± 30 14 C years, supplemented by the varying reservoir estimates of Stern and Lisiecki (2013) that provide an envelope of potential ages. HU2008029-12PC is bioturbated throughout. Sediments between the core base at 11.3 m and 4.6 m (LGM through HS1) comprise thin turbidites, plumites and hemipelagic sediments with Greenlandic provenance consistent with processes active at the Greenland Ice Sheet margin grounded at or near the shelf edge. Abundance spikes of planktic forams coincide with elevated abundance of benthic forams in assemblages indicative of chilled Atlantic Water, meltwater and intermittent marine productivity. IRD and IP 25 are rare in this interval, but brassicasterol, an indicator of marine productivity reaches and sustains low levels during the LGM. These biological characteristics are consistent with a sea-ice covered ocean experiencing periods of more open water such as leads or polynyas in the sea ice cover, with chilled Atlantic Water at depth, rather than full ice-shelf cover. They do not support the existence of a full Baffin Bay ice shelf cover extending from grounded ice on the Davis Strait. Initial ice retreat from the West Greenland margin is manifested by a pronounced lithofacies shift to bioturbated, diatomaceous mud with rare IRD of Greenlandic origin at 467 cm (16.2 cal ka BP; ∆ R = 140 yrs) within HS1. A spike in foraminiferal abundance and ocean warmth indicator benthic forams precedes the initial ice retreat from the shelf edge. At the end of HS1, IP 25 , brassicasterol and benthic forams indicative of sea-ice edge productivity increase, indicating warming interstadial conditions. Within the Bolling/Allerod interstadial a strong rise in IP 25 content and IRD spikes rich in detrital carbonate from northern Baffin Bay indicate that northern Baffin Bay ice streams were retreating and provides evidence for increased open water, advection of Atlantic Water in the West Greenland Current, and formation of an IRD belt along the W. Greenland margin.

We document the history of terms used to describe Heinrich (H-) layers and events and which mark major glaciological iceberg discharge events in the North Atlantic. We argue that the usage “Heinrich layer,” “Heinrich zone”, or “Heinrich event” should be restricted to only those sediments that can be ascribed to an origin from the Hudson Strait Ice Stream and the Laurentide Ice Sheet. We also argue that the commonplace understanding of these events---as dominated by massive iceberg discharges ---fails to include the earlier well-documented evidence that these events were also massive meltwater events linked to deposition along the North Atlantic Mid-Ocean Channel (NAMOC) in the Labrador Sea. We make five recommendations for future usage of “Heinrich events,” which include: restricting the usage to those events that can be mineralogically/geochemically linked to Hudson Strait; abandoning the term “Heinrich stadial”; and promote local terminology for “ice rafted events” that may be correlated, or not, with Hudson Strait Heinrich events based on calibrated radiocarbon dates or other appropriate chronological markers.