Annually resolved North Atlantic marine climate over the last millennium

Abstract

Owing to the lack of absolutely dated oceanographic information before the modern instrumental period, there is currently significant debate as to the role played by North Atlantic Ocean dynamics in previous climate transitions (for example, Medieval Climate Anomaly-Little Ice Age, MCA-LIA). Here we present analyses of a millennial-length, annually resolved and absolutely dated marine δ18O archive. We interpret our record of oxygen isotope ratios from the shells of the long-lived marine bivalve Arctica islandica (δ18O-shell), from the North Icelandic shelf, in relation to seawater density variability and demonstrate that solar and volcanic forcing coupled with ocean circulation dynamics are key drivers of climate variability over the last millennium. During the pre-industrial period (AD 1000–1800) variability in the sub-polar North Atlantic leads changes in Northern Hemisphere surface air temperatures at multi-decadal timescales, indicating that North Atlantic Ocean dynamics played an active role in modulating the response of the atmosphere to solar and volcanic forcing.

Variability in the Northern North Atlantic and Arctic Oceans Across the Last Two Millennia: A Review

“…Contrastingly, a higher-resolution diatom assemblage temperature from core record (MD99-2275) suggests a gradual cooling with a likely step change in surface temperatures between a relatively warm interval from 800 to 1300 CE to a relatively cooler interval~1350 CE to present, interpreted as the MCA-LIA transition (Jiang et al, 2005;Ran et al, 2011;Jiang et al, 2015; Figure 5j). Similar surface cooling trends are contained in alkenone reconstructions Sicre et al, 2011;Figure 5i) and an annually resolved δ 18 O shell (Reynolds et al, 2016; Figure 5k). Furthermore, reservoir ages based on mollusks and bivalves show an increase from ca.…”

“…Left panel shows sea/drift ice conditions (a) sea ice conditions in PS2641 BC/GC at Foster Bugt (Kolling et al, ); (b) drift ice recorded in the Denmark Strait JM96‐1206/2GC (Perner et al, ) North Iceland; (c) %Quartz from MD99‐2269 (Moros et al, ); sea ice biomarker (d) MD99‐2275 (Massé et al, ) and (e) MD99‐2269 (Cabedo‐Sanz et al, ); (f) April sea ice cover from diatom assemblages in the West Denmark Strait (MD99‐2322; Miettinen et al, );and (g) Haematite Stained Grains (HSG) transported from northwest Greenland to South Greenland (GS06‐144‐03; Alonso‐Garcia et al, ). Right panel shows oceanographic conditions (h) benthic foraminiferal assemblages at ~430 m, which are indicator of Atlantic Intermediate Waters (PS2641 BC/GC; (Perner et al, ), North Iceland upper water column conditions; (i) sea surface temperatures from alkenones (MD99–2275; Sicre et al, ; Sicre et al, ); (j) summer sea surface temperatures from diatom assemblages (Jiang et al, ; MD99–2275); (k) δ 18 O shell (black; Reynolds et al, ) and ∆ R (orange; Wanamaker et al, ) from Arctica islandica from the North Iceland shelf; (l) benthic assemblage from ~400‐m deep in the Northern Denmark Strait (JM96‐1206/2GC; Perner et al, ); (m) % planktonic foraminifera species N. pachyderma from the Eastern Labrador Sea (South Greenland; RAPiD‐35‐COM; Moffa‐Sánchez & Hall, ). Bold lines on raw data are weighted three‐point smoothing.…”

Reconstructing Past Seasonal to Multicentennial‐Scale Variability in the NE Atlantic Ocean Using the Long‐Lived Marine Bivalve MolluskGlycymeris glycymeris

“…GS/NAC = Gulf Stream/North Atlantic Current; EGC = East Greenland Current; PF = Polar Front; ESC = European Slope Current; SCC = Scottish Coastal Current. Figure adapted from Reynolds et al () and Inall et al ().…”

“…The development of sclerochronological records, incorporating the analyses of the physical and geochemical variations in the accretionary skeletal tissues of aquatic, marine, and terrestrial organisms (e.g., Hudson et al, ; Oschmann, ), provides the opportunity for the generation of absolutely dated and robustly calibrated reconstructions of past climate variability. Reconstructions derived from the analyses of marine bivalve growth increment width chronologies, constructed using dendrochronological cross‐dating techniques (e.g., Butler et al, ; Jones, ; Jones et al, ; Marchitto et al, ), and stable isotope (δ 18 O and δ 13 C; e.g., Reynolds et al, ; Schöne et al, ; Wanamaker et al, , ; Witbaard et al, ) and radioisotope ( 14 C; Wanamaker et al, ) time series developed from long‐lived marine bivalves, such as Arctica islandica and Glycymeris glycymeris , are now realized as robust archives of past marine variability. Hitherto, marine bivalve sclerochronological archives have provided robust reconstructions of past SWTs (Brocas et al, ; Mette et al, ; Reynolds et al, , ; Schöne et al, ), oceanic carbon dynamics (Schöne et al, ), marine radiocarbon reservoir ages (Wanamaker et al, ), coupled ocean and terrestrial ecosystem dynamics (Black, ; Black et al, ; Helama et al, ) and to investigate the mechanisms and drivers of ocean variability (Lohmann & Schöne, ; Reynolds et al, , ).…”

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“…At regional scales, new high-resolution oceanic observations (e.g. Reynolds et al, 2016) and syntheses (as in are under way and significant progresses on our understanding of past oceanic changes are expected in the coming years.…”