Holocene shifts in marine mammal distributions around Northern Greenland revealed by sedimentary ancient DNA

Abstract

Arctic marine ecosystems have undergone notable reconfigurations in response to Holocene climate and environmental changes. Yet our understanding of how marine mammal occurrence was impacted remains limited, due to their relative scarcity in the fossil record. We reconstruct the occurrence of marine mammals across the past 12,000 years through detections based on sedimentary ancient DNA from four marine sediment cores collected around Northern Greenland, and integrate the findings with local and regional environmental proxy records. Our findings indicate a close association between marine mammals at densities detectable in marine sediments and the deglaciation of high Arctic marine environments at the onset of the Holocene. Further, we identify air temperature and changes in sea ice cover as significant drivers of community change across time. Several marine mammals are detected in the sediments earlier than in the fossil record, for some species by several thousand years. During the Early-to-Mid Holocene, a period of warmer climate, we record northward distribution shifts of temperate and low-arctic marine mammal species. Our findings provide unique, long-term baseline data on the occurrence of marine mammals around Northern Greenland, enabling insights into past community dynamics and the effects of Holocene climatic shifts on the region's marine ecosystems.

Fig. 1. Sites and samples of the four marine sediment cores analyzed.

a Map of Greenland showing the localities of the cores, indicated by colored circles: Melville Bay 26G (red; 75° N; LK21-IC-st26-GC1); Hall Basin 24PC (purple; 82° N; Ryder19-24-PC1); Lincoln Sea 12-GC (blue; 83° N; Ryder19-12-GC1); North-East Greenland 73G (green; 79° N; DA17-NG-ST07-073G). Data from NOAA National Centers for Environmental Information, U.S. Department of Commerce, distributed as a U.S. Government Work (public domain). b Holocene air temperature reconstruction based on the oxygen isotopic signature (δ¹⁸O) at the Agassiz ice cap, as compared to the pre-industrial (1850-1900 CE) average^,. c Each sediment core was subsampled for DNA across its length. Triangles indicate the estimated median age of each sample based on the age-depth models of each core (Melville Bay 26G: this study; Hall Basin 24PC: this study; Lincoln Sea 12-GC; North East Greenland 73G); filled triangles indicate samples processed with hybridization capture; empty triangles indicate samples subjected to shotgun sequencing.

Fig. 2. Paleoceanographic reconstructions and DNA detections for marine sediment core Melville Bay 26G.

a Sea-ice biomarker IP₂₅ and (b) primary-productivity biomarkers brassicasterol and dinosterol are derived from marine sediment core GeoB19927-3. c High numbers of benthic foraminifera with preferred habitat of Atlantic-sourced waters indicate the influence of chilled Atlantic water, points represent counts per gram sediment (this study). d DNA concentrations of the DNA extracts of the sediment samples. e Marine mammal detections through hybridization capture. Silhouettes are shade-coded by present-day year-round occurrence (black), seasonal presence (gray), and absence (white) in the region; silhouettes were drawn by Anna Bang Kvorning. f Triangles show the estimated median age of each sample, with horizontal lines indicating confidence intervals. Samples with estimated median ages >11.6 cal ka BP likely represent a short time period at or just prior to the deglaciation of Melville Bay (estimated 11.6 ± 0.3 ka BP).

Fig. 3. Palaeoenvironmental reconstructions and DNA detections for marine sediment cores Hall Basin 24PC and Lincoln Sea 12-GC.

a Temperature reconstruction based on the oxygen isotopic signature (δ¹⁸O) at the Agassiz ice cap as compared to the pre-industrial (1850-1900 CE) average^,. b Evidence for the opening of Nares Strait (derived from core HLY03-01-05GC). c Sea-ice biomarker IP₂₅ and primary-productivity biomarker brassicasterol, derived from Lincoln Sea 12-GC. d–i DNA data from (d–f) Hall Basin 24 C are shown in purple; corresponding data from (g–i) Lincoln Sea 12-GC are shown in blue. d, g DNA concentrations of the DNA extracts of the sediment samples; e/h Marine mammal detections through hybridization capture; f, i Triangles show the estimated median age of each DNA sample, with horizontal lines indicating confidence intervals. Silhouettes are shade-coded by present-day year-round occurrence (black), seasonal presence (gray), and absence (white) in the region; silhouettes were drawn by Anna Bang Kvorning.

Fig. 4. Paleoceanographic reconstructions and DNA detections for marine sediment core North-East Greenland 73G.

a Sea-ice biomarker IP₂₅ and (b) primary productivity biomarkers brassicasterol and dinosterol are derived from marine sediment core PS93/025-2. c High numbers of benthic foraminifera with preferred habitat of Atlantic-sourced waters indicate the influence of Atlantic water, points represent counts per gram sediment (derived from marine sediment core North-East Greenland 73G). d DNA concentrations of the DNA extracts of the sediment samples. e Marine mammal detections through hybridization capture. Silhouettes are shade-coded by present-day year-round occurrence (black), seasonal presence (gray), and absence (white) in the region; silhouettes were drawn by Anna Bang Kvorning. f Triangles show the estimated median age of each DNA sample, with horizontal lines indicating confidence intervals.