Towards quantitative sea ice reconstructions in the northern North Atlantic: A combined biomarker and numerical modelling approach Juliane Müller a, ⁎, Axel Wagner a,b , Kirsten Fahl a , Ruediger Stein a , Matthias Prange b,c , Gerrit Lohmann a,b a Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany b University of Bremen, Germany c MARUM, Center for Marine Environmental Sciences, Bremen, Germany abstract article info Article history: Received 24 November 2010 Received in revised form 4 April 2011 Accepted 14 April 2011 Available online 2 May 2011 Editor: P. DeMenocal Keywords: Northern North Atlantic sea ice biomarkers IP 25 Ocean–sea ice model Organic geochemical analyses of marine surface sediments from the continental margins of East Greenland and West Spitsbergen provide for a biomarker-based estimate of recent sea ice conditions in the northern North Atlantic. By means of the sea ice proxy IP 25 and phytoplankton derived biomarkers (e.g. brassicasterol and dinosterol) we reconstruct sea ice and sea surface conditions, respectively. The combination of IP 25 with a phytoplankton marker (in terms of a phytoplankton marker-IP 25 index; PIP 25 ) proves highly valuable to properly interpret the sea ice proxy signal as an under- or overestimation of sea ice coverage can be circumvented. A comparison of this biomarker-based assessment of the sea ice distribution in the study area with (1) modern remote sensing data and (2) numerical modelling results reveal a good agreement between organic geochemical, satellite and modelling observations. The reasonable simulation of modern sea ice conditions by means of a regional ocean–sea ice model demonstrates the feasibility to effectively integrate the complex atmospheric and oceanic circulation features as they prevail in the study area. The good correlation between modelled sea ice parameters and the biomarker-based estimate of sea ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross-evaluation. This combinatory approach may provide a first step towards quantitative sea ice reconstructions by means of IP 25 . Future IP 25 studies on marine surface sediments from the Arctic realm, however, are recommended to extend and validate this new attempt of using IP 25 in combination with a phytoplankton marker as a quantitative measure for sea ice reconstructions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Arctic sea ice is a pivotal element of the global climate as it influences the heat and moisture exchange between the ocean and the atmosphere. Furthermore it significantly affects the oceanic heat transfer and salinity regulation between southern and northern latitudes, thus impacting on the thermohaline circulation in the northern North Atlantic (e.g. Dieckmann and Hellmer, 2003; Rudels, 1996). Information on modern Arctic sea ice conditions derive mainly from remote sensing data (e.g. Gloersen et al., 1992; Spreen et al., 2008) and research vessel observations (for instance, sediment trap and buoy data; e.g. Bauerfeind et al., 2005; Fahl and Nöthig, 2007; Perovich et al., 2009; see Eicken et al., 2009 for further field techniques) and allow for the monitoring of the most recent development of sea ice coverage in higher latitudes. Besides the concern about its future development, the currently observed retreat of Arctic sea ice, however, also prompts a gaining interest in past (natural) variations of the sea ice extent in the Arctic Ocean. Most studies on the palaeodistribution of sea ice are commonly based on sedimentological data (Knies et al., 2001; Spielhagen et al., 2004) and microfossils (e.g. Carstens and Wefer, 1992; Koç et al., 1993; Matthiessen et al., 2001; Polyak et al., 2010; for a recent review see Stein, 2008). In particular, sea ice associated (sympagic) organisms (e.g. pennate ice diatoms; Horner, 1985) which contribute remarkably to the primary production in the marine Arctic ice environment (Gosselin et al., 1997; Gradinger, 2009), are frequently used for reconstructing sea ice conditions (Abelmann, 1992; Justwan and Koç, 2008; Koç et al., 1993; Kohly, 1998). However, it has also been shown previously that the preservation of fragile siliceous diatom frustules can be relatively poor in surface sediments from the Arctic realm and the same is also true (if not worse) for calcareous- walled microfossils, thus limiting their application potential (Kohly, 1998; Matthiessen et al., 2001; Schlüter and Sauter, 2000; Steinsund and Hald, 1994). In recent decades, the organic geochemical investigation of marine sediments for specific molecular tracers (biomarkers), which are indicative of the type of organic matter they are derived from, has Earth and Planetary Science Letters 306 (2011) 137–148 ⁎ Corresponding author. E-mail address: juliane.mueller@awi.de (J. Müller). 0012-821X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2011.04.011 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl