Available online xxxx Editor: D. Vance Keywords: sea ice Arctic proxy IP 25 biomarker paleoclimateAnalysis of >100 surface sediments from across the Barents Sea has shown that the relative abundances of the mono-unsaturated sea ice diatom-derived biomarker IP 25 and a tri-unsaturated highly branched isoprenoid (HBI) lipid (HBI III) are characteristic of the overlying surface oceanographic conditions, most notably, the location of the seasonal sea ice edge. Thus, while IP 25 is generally limited to locations experiencing seasonal sea ice, with higher abundances found for locations with longer periods of ice cover, HBI III is found in sediments from all sampling locations, but is significantly enhanced in sediments within the vicinity of the retreating sea ice edge or marginal ice zone (MIZ). The response of HBI III to this well-defined sea ice scenario also appears to be more selective than that of the more generic phytoplankton biomarker, brassicasterol. The potential for the combined analysis of IP 25 and HBI III to provide more detailed assessments of past sea ice conditions than IP 25 alone has been investigated by quantifying both biomarkers in three marine downcore records from locations with contrasting modern sea ice settings. For sediment cores from the western Barents Sea (intermittent seasonal sea ice) and the northern Norwegian Sea (ice-free), high IP 25 and low HBI III during the Younger Dryas (ca. 12.9-11.9 cal. kyr BP) is consistent with extensive sea cover, with relatively short periods of icefree conditions resulting from late summer retreat. Towards the end of the YD (ca. 11.9-11.5 cal. kyr BP), a general amelioration of conditions resulted in a near winter maximum ice edge scenario for both locations, although this was somewhat variable, and the eventual transition to predominantly ice-free conditions was later for the western Barents Sea site (ca. 9.9 cal. kyr BP) compared to NW Norway (ca. 11.5 cal. kyr BP). For both locations, coeval elevated HBI III (but absent IP 25 ) potentially provides further evidence for increased Atlantic Water inflow during the early Holocene, but this interpretation requires further investigation. In contrast, IP 25 and HBI III data obtained from a core from the northern Barents Sea demonstrate that seasonal sea ice prevailed throughout the Holocene, but with a gradual shift from winter ice edge conditions during the early Holocene to more sustained ice cover in the Neoglacial; a directional shift that has undergone a reverse in the last ca. 150 yr according to observational records. Our combined surface and downcore datasets suggest that combined analysis of IP 25 and HBI III can provide information on temporal variations in the position of the maximum (winter) Arctic sea ice extent, together with insights into sea ice seasonality by characterisation of the MIZ. Combining IP 25 with HBI III in the form of the previously proposed PIP 25 index yields similar outcomes to those obtained using brassicasterol as the phytoplankton marker. Importantly, however, some proble...

Semi-quantitative estimates of paleo Arctic sea ice concentration based on source-specific highly branched isoprenoid alkenes: A further development of the PIP25 index Smik, L Please cite this article as: Smik, L., Cabedo-Sanz, P., Belt, S.T., Semi-quantitative estimates of paleo Arctic sea ice concentration based on source-specific highly branched isoprenoid alkenes: a further development of the PIP 25 index, Organic Geochemistry (2015), doi: http://dx.

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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