Tracking Holocene drift-ice limits on the northwest–southwest Iceland shelf: Comparing proxy data with observation and historical evidence

We detail variations in the weight percent (wt%) of quartz, a proxy for drift ice, in fifteen marine sediment cores from the northwest, west, and southwest Iceland shelf throughout the past 10 cal ka BP. We present the first map of iceberg distributions in Iceland waters between 1983 and 2011 and a new compilation of sea-ice records in the century from 850 to 1950 CE. The wt% of quartz, determined by quantitative X-ray diffraction (qXRD) analysis, is used to evaluate changes in the importation of drift ice. Small wt% of quartz were added to milled basalt (0% quartz), and to a mixture of non-clay and clay minerals; the qXRD method replicated 0 percent quartz, while measured 1&ndash;3 percent quartz always resulted in a &ldquo;presence&rdquo; estimate. The outer sites in the northwest sector lie close to the average position of the sea-ice margin between 1870 and 1920 CE; the southwest shelf sites lie south of this limit. Transects of cores along the H&uacute;nafl&oacute;i and Dj&uacute;p&aacute;ll troughs indicate that the traces of drift ice decrease rapidly landward from the outer sites. The cores from the west/southwest of Iceland have limited amounts of quartz, generally possibly limited incursions of drift ice.</p

Near-universal trends in brGDGT lipid distributions in nature

Bacterial brGDGT lipids are a prevalent tool in studies of terrestrial paleoclimate. Their distributions correlate empirically with environmental temperature and pH, and their ubiquity in terrestrial, freshwater, and marine environments gives them wide applicability. Whether correlations with temperature and pH emerge due to a physiological response of source organisms and/or a shift in bacterial community composition remains an open question with important implications for proxy development and application. We applied a newly described technique for grouping brGDGTs to a globally compiled dataset (n = 3129) consisting of all modern sample media known to host brGDGTs. We found strong resemblances in the relationships between brGDGT fractional abundances and both temperature and pH across nearly all sample types examined. We also found near-universal connections between the brGDGTs themselves. Given the markedly different bacterial communities expected to inhabit these settings, these widespread relationships may suggest physiological and/or biochemical bases for observed brGDGT distributions. &nbsp;</p

Intact Polar brGDGTs in Arctic Lake Catchments: Implications for Lipid Sources and Paleoclimate Applications

Paleotemperature histories derived from lake sediment archives provide valuable context for modern and future climate changes. Branched glycerol dialkyl glycerol tetraether (brGDGT) lipids are a valuable tool in such pursuits due to their empirical correlation with temperature and near ubiquity in nature. However, the relative contributions of terrestrial and lacustrine sources of brGDGTs to lake sediments is site-dependent and difficult to constrain. Here, we explored the potential for intact brGDGTs—the complete lipids with polar head groups (HGs) still attached—to provide insight into the sources of brGDGTs on the landscape and their contributions to the sedimentary record in a set of Arctic lakes. We measured core and intact brGDGTs in soils, surface and downcore sediments, water filtrates, and sediment traps across five lake catchments in the Eastern Canadian Arctic, with an emphasis on Lake Qaupat (QPT), Baffin Island. Soils were dominated by brGDGTs with a monoglycosyl (1G) HG, while lacustrine samples contained more phosphohexose (PH) brGDGTs, providing evidence for in situ brGDGT production in both settings. Core- and PH-brGDGT-IIIa were more abundant in sediments than in the soils or water column, implying an additional post-depositional source of brGDGTs. A hierarchical clustering analysis indicated that core brGDGTs in Lake QPT sediments were largely lacustrine in origin, while 1G-brGDGTs were primarily soil-derived. Additionally, we found evidence for preservation of intact brGDGTs—especially 1G-brGDGTs—downcore on thousand-year timespans, though in situ production deeper in the sediment column cannot be ruled out. Finally, we explored the possibility of reconstructing 1G-brGDGT-derived soil temperatures and core-brGDGT-derived lake temperatures in tandem from sedimentary archives

The onset of neoglaciation in Iceland and the 4.2 ka event

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.Peer Reviewe

A Holocene history of climate, fire, landscape evolution, and human activity in northeastern Iceland

Paleoclimate reconstructions across Iceland provide a template for past changes in climate across the northern North Atlantic, a crucial region due to its position relative to the global northward heat transport system and its vulnerability to climate change. The roles of orbitally driven summer cooling, volcanism, and human impact as triggers of local environmental changes in the Holocene of Iceland remain debated. While there are indications that human impact may have reduced environmental resilience during late Holocene summer cooling, it is still difficult to resolve to what extent human and natural factors affected Iceland's late Holocene landscape instability. Here, we present a continuous Holocene fire record of northeastern Iceland from proxies archived in St&oacute;ra Vi&eth;arvatn sediment. We use pyrogenic polycyclic aromatic hydrocarbons (pyroPAHs) to trace shifts in fire regimes, paired with continuous biomarker and bulk geochemical records of soil erosion, lake productivity, and human presence. The molecular composition of pyroPAHs and a wind pattern reconstruction indicate a naturally driven fire signal that is mostly regional. Generally low fire frequency during most of the Holocene significantly increased at 3&thinsp;ka and again after 1.5&thinsp;ka&thinsp;BP before known human settlement in Iceland. We propose that shifts in vegetation type caused by cooling summers over the past 3&thinsp;kyr, in addition to changes in atmospheric circulation, such as shifts in North Atlantic Oscillation (NAO) regime, led to increased aridity and biomass flammability. Our results show no evidence of faecal biomarkers associated with human activity during or after human colonisation in the 9th century CE. Instead, faecal biomarkers follow the pattern described by erosional proxies, pointing toward a negligible human presence and/or a diluted signal in the lake's catchment. However, low post-colonisation levels of pyroPAHs, in contrast to an increasing flux of erosional bulk proxies, suggest that farming and animal husbandry may have suppressed fire frequency by reducing the spread and flammability of fire-prone vegetation (e.g. heathlands). &nbsp;</p

Spatiotemporal variation of modern lake, stream, and soil water isotopes in Iceland

As global warming progresses, changes in high-latitude precipitation are expected to impart long-lasting impacts on Earth systems, including glacier mass balance and ecosystem structures. Reconstructing past changes in high-latitude precipitation and hydroclimate from networks of continuous lake records offers one way to improve forecasts of precipitation and precipitation&ndash;evaporation balances, but these reconstructions are currently hindered by the incomplete understanding of controls on lake and soil water isotopes. Here, we study the distribution of modern water isotopes in Icelandic lakes, streams, and surface soils collected in 2002, 2003, 2004, 2014, 2019, and 2020 to understand the geographic, geomorphic, and environmental controls on their regional and interannual variability. We find that lake water isotopes in open-basin (through-flowing) lakes reflect local precipitation, with biases toward the cold season, particularly in lakes with sub-annual residence times. Closed-basin lakes have water isotope and deuterium excess values consistent with evaporative enrichment. Interannual and seasonal variabilities of lake water isotopes at repeatedly sampled sites are consistent with instrumental records of winter snowfall; summer relative humidity; and atmospheric circulation patterns, such as the North Atlantic Oscillation. Summer surface soil water isotopes span the entire range of seasonal precipitation values in Iceland and appear to be consistently overprinted by evaporative enrichment, which can occur throughout the year, although the sampling depths were shallower than rooting depths for many plant types. This dataset provides new insight into the functionality of water isotopes in Icelandic environments and offers renewed possibilities for optimized site selection and proxy interpretation in future paleohydrological studies on this North Atlantic outpost. &nbsp;</p

Variability in drift ice export from the Arctic Ocean to the North Icelandic Shelf over the last 8000 years: A multi-proxy evaluation

publisher: Elsevier articletitle: Variability in drift ice export from the Arctic Ocean to the North Icelandic Shelf over the last 8000 years: A multi-proxy evaluation journaltitle: Quaternary Science Reviews articlelink: http://dx.doi.org/10.1016/j.quascirev.2016.06.012 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved

Candida Endophthalmitis [case reports]

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/Open36 ára gömul áður hraust kona leitaði til augnlæknis vegna mánaðarsögu um versnandi sjón á vinstra auga. Hún hafði orðið uppvís að sprautumisnotkun sex mánuðum fyrr. Augað var verkjalaust og án roða. Sjón mældist 0,1 á vinstra auga en 1,0 á því hægra. Augnbotn vinstra augans er sýndur á mynd 1, en blæðing sást við sjóntaugina og lítill hvítleitur blettur á makúlu. Einnig mátti greina einstaka frumur í forhólfi augans og hvítleitar þéttingar í glerhlaupi sem sjást á mynd 2. Hver er líklegasta greiningin, hverjar eru helstu mismunagreiningar og hver er besta meðferðin

Global compilation of brGDGT lipid distributions, temperature, and pH across a dozen sample types

Lipid and environmental data were compiled from previously published datasets of modern samples that used the most recent chromatographic methods that separate 5- and 6-methyl isomers. The compiled dataset (n = 3129) consisted of bone (n = 202), groundwater (n = 7), lake water meso/microcosm (n = 36), lake surface sediment (n = 343), lake water SPM (n = 228, including sediment traps (n = 115) and water filtrates (n = 113)), low DO lake water SPM (n = 138, including sediment traps (n = 29) and water filtrates (n = 109)), authigenic carbonates from a marine methane cold seep (n = 13), marine surface sediment (n = 325, including deep ocean trench sediments (n = 31)), marine SPM (water filtrates, n = 25), peat (n = 473), riverine surface sediments (n = 71) and SPM (water filtrates, n = 85), and soil (n = 1183, including permafrost active layer (n = 17)). Data from other sample media, including hot springs, speleothems, and hydrothermal vents, could not be included as these studies did not separate the 5- and 6-methyl isomers. Fractional abundances (FAs) were calculated according to Raberg et al., (2021). We compiled the brGDGT FAs and, to the best of our ability, associated temperature and pH values from previously published datasets. We selected temperature parameters that were widely supported in the literature when possible. Where a consensus had yet to be reached (e.g., marine sediments), we selected standardizable and accessible parameters (e.g., sea surface temperatures). These selections are not intended to opine on these areas of research, only to allow for broad comparison with other sample types in this study