DOI: 10.1594/pangaea.981127
title: Biomarkers, total organic carbon and planktonic foraminifera abundances in gravity core MSM101_44-3 from St Anns Basin, Scotian Shelf

description: Holocene sea ice and marine productivity reconstructions based on a sediment core from the northeast Scotian Shelf. The gravity core MSM101_44-3 was retieived during R/V Maria S. Merian expedition MSM101 from St. Anns Basin (45°46.651'N 58°31.967'W; 274 m water depth) in 2021 (Schneider et al., 2021). For sea-ice and productivity reconstruction of the past 10,100 years BP, biomarkers representing sea-ice algae productivity (IP25, HBI II), open-water phytoplankton productivity (dinosterol, brassicasterol), marginal ice zone (HBI III (Z), HBI III (E)), and terrigenous input (campesterol), as well as total organic carbon (TOC) and planktonic foraminifera abundances were analyzed.. The scope of the underlying study was to investigate (1) the response of sea ice to regional changes in oceanic and atmospheric conditions during the Holocene, (2) the linkage of regional Holocene sea-ice dynamics, marine productivity, and terrigenous inputs with oceanographic changes, and (3) the effects of meltwater events on sea-ice cover and primary productivity on the Scotian Shelf during the Early Holocene.
description: The age model of core MSM101_44-3 is based on 10 Accelerator Mass Spectrometer 14C measurements at Leibniz-Laboratory of Kiel University of mixed benthic foraminifera. It was constrained with a Bayesian Poisson-process deposition model using OxCal v4.4.4. (Ramsey, 2008. 2009) and the Marine20 dataset (Heaton et al., 2020) with a local marine reservoir offset of -86 (±66) years (McNeely et al., 2006).To determine the TOC content, sediment subsamples were treated with ethanol and hydrochloric acid and heated afterwards. The measurement was performed on an ELTRA CS-800 carbon-sulphur determinator. Reproducibility measurements (n=11) and standards were measured for quality control (σ=&lt;0.01 wt%) and instrument stability.Biomarker analyses were performed on about 5 g of freeze-dried sediment. Internal standards 7-hexylnonadecane (7-HND for HBIs) and 5α-androstan-3β-ol (androstanol for sterols) were added prior extraction for quantification and quality control reasons. Biomarker subsamples were extracted by sonication using 30 ml dichlormethane:methanol (2:1 v/v) as a solvent and centrifuged afterwards (2000 rpm, 3 min). The HBIs (IP25, HBI II, HBI III (Z), HBI III (E)) and sterols (dinosterol, brassicasterol, campesterol) were eluted using 5 ml n-hexane and 9 ml ethylacetat:n-hexane (20:80 v/v), respectively, suing open-column chromatography with SiO2 as stationary phase. Sterols were derivatized with 200 µl bis-trimethylsilyl-trifluoracet-amid (60°C, 2h).Hydrocarbon and sterol concentrations were measured with a gas chromatograph coupled to a mass selective detector at the Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research in Bremerhaven. For detailed instrument settings and compound identification see Fahl and Stein (2012).All individual biomarker concentrations were calculated in relation to the internal standard and normalized to both TOC (ng/gTOC) and weight of sediment sample (ng/gSed).Accumulation rates were calculated for all biomarkers and TOC using the following equation (e.g., Stein and Macdonald, 2004):SAR = SR x DBD (1)TOC AR = SAR x TOC/100 (2)BM AR = SAR x BM conc. (3)with SAR = sediment accumulation rate (g/cm2/ka), SR = sedimentation rate (cm/ka), DBD = dry bulk density (g/cm3), TOC = total organic carbon (%), BM conc. = biomarker concentration (ng/gSed), TOC AR = total organic carbon accumulation rate (g/cm2/ka), BM AR = biomarker accumulation rate (ng/cm2/ka).The PIP25 index (Müller et al., 2011) was calculated as:PIP25 = IP25/(IP25 + (BM phyt x c)) (4)with BM phyt = phytoplankton biomarker concentration (ng/gSed), IP25 = IP25 concentration (ng/gSed), c = balance factor determined from the ratio of IP25 and mean sterol concentration, PIP25 = PIP25 index. Three PIP25 index calculations were performed with dinosterol (PDIP25), brassicasterol (PBIP25) and HBI III (Z) (PIIIIP25) as the phytoplankton biomarkers.The HBI fingerprinting index, in short H-index (Brown et al., 2014), was calculated using the following equation by Koch et al. (2020):H-index [%] = (HBI III (Z)/∑(IP25 + HBI II + HBI III (Z))) x 100 (5)with IP25, HBI II and HBI III (Z) equal their respective biomarker concentration (ng/gSed).About 30 g of wet sediment were washed and sieved at 150 µm for planktonic foraminifera counting. To calculate the total amount of planktonic foraminifera, the counts of planktonic foraminifera &gt;150 µm were normalized to the weight of sediment sample (ind/gSed).