Figure 5. Proxy data of sediment core JM11-FI-19PC 90 kyr b2k to present.

(a) δ¹⁸O measured in planktic foraminiferal species N. pachyderma s (‰ versus (vs) Pee Dee Belemnite (PDB)), (b) MS (10⁻⁶ SI units), (c) TOC (% of dry weight sediment), (d) δ¹³C_org (‰ vs PDB), (e) IP₂₅ (μg g⁻¹ TOC, black) and (f) (μg g⁻¹ sediment (sed.), orange), (g) brassicasterol (μg g⁻¹ TOC, black) and (h) (μg g⁻¹ (i) calculated index P_BIP₂₅ (brassicasterol), (j) dinosterol (μg g⁻¹ black) and (k) (μg g⁻¹, (l) calculated index P_DIP₂₅ (dinosterol), (m) relative abundance of diatom species Fragilariopsis oceanica (Cleve) Hasle (%, blue), (n) relative abundance of diatom species Thalassiosira oestrupii (Ostenfeld) Hasle (%, magenta), (o) diatom flux (10⁰⁵ frustules (fr.) per cm² per kyr, black) and (p) diatom concentrations (10⁰⁵ frustules per g sed., orange), and MIS are shown. Vertical lines in IP₂₅, brassicasterol and P_BIP₂₅ mark the cutoff values of sea ice cover stages²⁶,²⁷. Legend at the bottom of the figure show cutoff values of IP₂₅ (μg g⁻¹ TOC), brassicasterol (μg g⁻¹ TOC) and P_BIP₂₅ as criteria of the interpretation of IP₂₅, brassicasterol, dinosterol, P_BIP₂₅ and P_DIP₂₅ in terms of degree of sea ice cover. Brassicasterol values (as proxy for open-water phytoplankton productivity) are in great accordance with the dinosterol numbers, therefore only values for brassicasterol are shown. Zero or near-zero concentrations of both IP₂₅ as well as phytoplankton biomarkers are indicative for a closed (spring) sea ice cover (PIP₂₅ in general is indeterminable and per definition set to ‘1' (refs ¹⁵, ²⁶); see P_BIP₂₅ and P_DIP₂₅ during H1, marked by blue stars). Arrows mark events of increased productivity during IS cooling phases (see text for explanation). H, H-event; ‘not enough diatoms preserved', in these intervals there were not enough diatoms preserved to be quantified after the set criteria (see Methods).