Sea Ice Versus Storms: What Controls Sea Salt in Arctic Ice Cores?

Abstract

The sea ice surface is thought to be a major source of sea salt aerosol, suggesting that sodium records of polar ice cores may trace past sea ice extent. Here we test this possibility for the Arctic, using a chemical transport model to simulate aerosol emission, transport, and deposition in the satellite era. Our simulations suggest that sodium records from inland Greenland ice cores are strongly influenced by the impact of meteorology on aerosol transport and deposition. In contrast, sodium in coastal Arctic cores is predominantly sourced from the sea ice surface and the strength of these aerosol emissions controls the ice core sodium variability. Such ice cores may therefore record decadal to centennial scale Holocene sea ice changes. However, any relationship between ice core sodium and sea ice change may depend on how sea ice seasonality impacts sea salt emissions. Field‐based observations are urgently required to constrain this.

Decadal-scale progression of the onset of Dansgaard–Oeschger warming events

“…As pointed out by Schüpbach et al (2018), on centennial to millennial timescales, changes in the central Asian dust source strengths by a factor of approximately 4 are needed to explain the complete amplitude between stadials and interstadials observed in the ice cores, as further supported by downwind sediment records (Porter and Zhisheng, 1995;Jacobel et al, 2017). The deflation of the dust from the central Asian source regions is strongly dependent on location of the westerly jet (Nagashima et al, 2011;Roe, 2009) that under current conditions covaries with the East Asian Summer Monsoon on seasonal timescales (Schiemann et al, 2009). During the glacial conditions, the westerly jet was located further south than today, leading to more frequent or even permanent conditions for dust emission (Chiang et al, 2015;Nagashima et al, 2011).…”

“…Under current conditions, aerosol transport models point at the emission from blowing snow from winter sea ice as the dominant source of sea-salt aerosol for Greenland in winter and suggest that this source is responsible for a large fraction of the seasonal variability seen in ice-core records (Huang and Jaeglé, 2017;Rhodes et al, 2017). However, on interannual timescales, the influence of the atmospheric transport and deposition dominates the variability at the central Greenland sites for recent times, due to the overall low contribution of sea-ice-derived aerosol to the total sea-salt aerosol budget (Rhodes et al, 2018). Under glacial conditions, the extended multi-year seaice cover moves both sources of open-ocean and sea-icederived sea-salt aerosols further away from the ice-core sites.…”

“…Mineralogy and isotopic composition of mineral dust aerosol from central Greenland indicate that its dominant glacial sources are the central Asian Taklamakan and Gobi deserts (Biscaye et al, 1997;Svensson et al, 2000). Large dust storms occurring during spring can lift dust up into the westerly jet stream where it is transported over long ranges and at high altitudes (Sun et al, 2001;Roe, 2009). The dust emission and subsequent entrainment into the jet are strongly dependent on the specific synoptic circulation in the area which itself is governed by the latitudinal position of the westerly jet (Nagashima et al, 2011;Roe, 2009).…”

“…Large dust storms occurring during spring can lift dust up into the westerly jet stream where it is transported over long ranges and at high altitudes (Sun et al, 2001;Roe, 2009). The dust emission and subsequent entrainment into the jet are strongly dependent on the specific synoptic circulation in the area which itself is governed by the latitudinal position of the westerly jet (Nagashima et al, 2011;Roe, 2009). Under current conditions, the position of the westerly jet over central Asia varies seasonally, changing from south to north of the Tibetan plateau during late spring, in unison with the northward movement of the East Asian Summer Monsoon rain belt (Schiemann et al, 2009;Yihui and Chan, 2005).…”

Decadal-scale progression of Dansgaard-Oeschger warming events

“…Under current conditions, aerosol transport models point at the emission from blowing snow from winter sea ice as the dominant source of sea-salt aerosol for Greenland in winter and suggest that this source is responsible for a large fraction of the seasonal variability seen in ice-core records (Huang and Jaeglé, 2017;Rhodes et al, 2017). However, on inter-annual time scales the influence of the atmospheric transport and deposition dominates the variability at the central Greenland sites for recent times, due to the overall low contribution of sea-ice-derived aerosol to the total sea-salt aerosol budget (Rhodes et al, 2018). Under glacial conditions, the extended multi-year sea-ice cover moves both sources of open-ocean and sea-ice-derived sea-salt aerosols further away from the ice-core sites.…”