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Abstract. 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 Stóra Viðarvatn 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 ka and again after 1.5 ka BP before known human settlement in Iceland. We propose that shifts in vegetation type caused by cooling summers over the past 3 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). Overall, our results describe a fire frequency heavily influenced by long-term changes in climate through the Holocene. They also suggest that human colonisation had contrasting effects on the local environment by lowering its resilience to soil erosion while increasing its resilience to fire. 

Abstract. The North Water Polynya (NOW, Inuktitut: Sarvarjuaq; Kalaallisut:Pikialasorsuaq), Baffin Bay, is the largest polynya and one of the most productive regionsin the Arctic. This area of thin to absent sea ice is a critical moisturesource for local ice sheet sustenance and, coupled with the inflow ofnutrient-rich Arctic Surface Water, supports a diverse community of Arcticfauna and indigenous people. Although paleoceanographic records provideimportant insight into the NOW's past behavior, it is critical that webetter understand the modern functionality of paleoceanographic proxies. Inthis study, we analyzed lipid biomarkers, including algal highly branchedisoprenoids and sterols for sea ice extent and pelagic productivity andarchaeal glycerol dibiphytanyl glycerol tetraethers (GDGTs) for ocean temperature, in a set of modern surface sedimentsamples from within and around the NOW. In conjunction with previouslypublished datasets, our results show that all highly branched isoprenoidsexhibit strong correlations with each other and not with sterols, whichsuggests a spring or autumn sea ice diatom source for all highly branched isoprenoids (HBIs) rather than acombination of sea ice and open-water diatoms as seen elsewhere in theArctic. Sterols are also highly concentrated in the NOW and exhibitstatistically higher concentrations here compared to sites south of the NOW,consistent with the order of magnitude higher primary productivity observedwithin the NOW relative to surrounding waters in spring and summer months.Finally, our local temperature calibrations for GDGTs and OH-GDGTs reducethe uncertainty present in global temperature calibrations but alsoidentify some additional variables that may be important in controllingtheir local distribution, such as nitrate availability and dissolved oxygen.Collectively, our analyses provide new insight into the utility of theselipid biomarker proxies in high-latitude settings and will help provide arefined perspective on the past development of the NOW with theirapplication in downcore reconstructions.