A 120 000-year record of sea ice in the North Atlantic?

Abstract

Abstract. Although it has been demonstrated that the speed and magnitude of the recent Arctic sea ice decline is unprecedented for the past 1450 years, few records are available to provide a paleoclimate context for Arctic sea ice extent. Bromine enrichment in ice cores has been suggested to indicate the extent of newly formed sea ice areas. Despite the similarities among sea ice indicators and ice core bromine enrichment records, uncertainties still exist regarding the quantitative linkages between bromine reactive chemistry and the first-year sea ice surfaces. Here we present a 120 000-year record of bromine enrichment from the RECAP (REnland ice CAP) ice core, coastal east Greenland, and interpret it as a record of first-year sea ice. We compare it to existing sea ice records from marine cores and tentatively reconstruct past sea ice conditions in the North Atlantic as far north as the Fram Strait (50–85∘ N). Our interpretation implies that during the last deglaciation, the transition from multi-year to first-year sea ice started at ∼17.5 ka, synchronously with sea ice reductions observed in the eastern Nordic Seas and with the increase in North Atlantic ocean temperature. First-year sea ice reached its maximum at 12.4–11.8 ka during the Younger Dryas, after which open-water conditions started to dominate, consistent with sea ice records from the eastern Nordic Seas and the North Icelandic shelf. Our results show that over the last 120 000 years, multi-year sea ice extent was greatest during Marine Isotope Stage (MIS) 2 and possibly during MIS 4, with more extended first-year sea ice during MIS 3 and MIS 5. Sea ice extent during the Holocene (MIS 1) has been less than at any time in the last 120 000 years.

Rapid reductions and millennial-scale variability in Nordic Seas sea ice cover during abrupt glacial climate changes

“…Sea Ice Proxy Evidence from the RECAP Ice Core. To assist the interpretation of our marine sea ice records, we enhanced the temporal resolution of the RECAP Br enr -based sea ice record between 32 and 41 ka, previously presented at a lower resolution for the last 120 ky (32). The Br enr proxy is based on the bromineto-sodium mass ratio of ice normalized to that of seawater, and is considered as reflecting first-year (i.e., seasonal) sea ice conditions in the marine aerosol source area (32, 44, 45) (SI Appendix, Materials and Methods).…”

“…Bromine recycling processes occurring over seasonal (first year) sea ice formation add photochemically derived bromine to the sea salt-derived aerosol inventory of the overlying atmosphere, consequently leading to increased Br enr values in snow and ice precipitating nearby (46). Processes associated with aerosol transport and deposition might additionally influence the Br enr signals in ice cores (32,47). Nevertheless, an enhanced Br enr (>1) in Greenland ice cores is considered to reflect extensive seasonal sea ice in the marine aerosol source area (32,45).…”

High-frequency climate variability in the Holocene from a coastal-dome ice core in east-central Greenland

“…2). Polar ice core water isotope records are correlated to condensation temperature at the time of precipitation (Dansgaard, 1964;Dansgaard et al, 1973;Craig and Gordon, 1965;Merlivat and Jouzel, 1979;Jouzel and Merlivat, 1984;Jouzel et al, 1997) and integrate across regional ocean and atmospheric circulation patterns and sea surface conditions along the moisture transport pathway (Johnsen et al, 2001;Holme et al, 2019).…”

5 kyr of fire history in the High North Atlantic Region: natural variability and ancient human forcing

“…Seven day long back trajectories calculated with HYSPLIT model over the period 2006-2019 suggest that the higher frequency of trajectories come from the nearby areas with respect to the Renland site ( Figure 1), as also evidenced by Simonsen et al (2019) and Maffezzoli et al (2019) studying insoluble dust and sea ice respectively. In addition to the Renland ice cap surrounding area, the coastal area immediately on the North of the Renland site appears to be the most probable source region.…”

“…The core was stored frozen and shipped to Europe, where it was cut at AWI (Alfred-Wegener Institute, Bremerhaven, Germany) and processed at the Centre for Ice and Climate (Niels Bohr Institute, University of Copenhagen, Denmark). The samples analyzed for levoglucosan were collected discretely every 55 cm from a continuous ice core melting system (Bigler et al, 2011) as part of the Continuous Flow Analysis (CFA) campaign conducted at the University of Copenhagen in autumn 2015 (Maffezzoli et al, 2019;Simonsen et al, 2019), while BC and NH 4 + were measured continuously. After collection, the discrete samples were immediately frozen at -20°C and kept in the dark until analysis.…”