Exploring ice core sea ice proxies through process-based modelling

Mapping Intimacies ◽

10.5194/egusphere-egu2020-9013 ◽

2020 ◽

Author(s):

Rachael Rhodes ◽

Xin Yang ◽

Eric Wolff

Keyword(s):

Sea Ice ◽

Atmospheric Chemistry ◽

Ice Core ◽

Ice Cores ◽

Sea Salt ◽

Atmospheric Composition ◽

The Arctic ◽

Sea Salt Aerosol ◽

Aerosol Emission ◽

The Impact

It is important to understand the magnitude and rate of past sea ice changes, as well as their timing relative to abrupt shifts in other components of Earth&#8217;s climate system. Furthermore, records of past sea ice over the last few centuries are urgently needed to assess the scale of natural (internal) variability over decadal timescales. By continuously recording past atmospheric composition, polar ice cores have the potential to document changing sea ice conditions if atmospheric chemistry is altered. &#160;Sea salt aerosol, specifically sodium (Na), and bromine enrichment (Brenr, Br/Na enriched relative to seawater ratio) are two ice core sea ice proxies suggested following this premise.Here we aim to move beyond a conceptual understanding of the controls on Na and Brenr in ice cores by using process-based modelling to test hypotheses. We present results of experiments using a 3D global chemical transport model (p-TOMCAT) that represents marine aerosol emission, transport and deposition. Critically, the complex atmospheric chemistry of bromine is also included. Three fundamental issues will be examined: 1) the partitioning of Br between gas and aerosol phases, 2) sea salt aerosol production from first-year versus multi-year sea ice, and 3) the impact of increased acidity in the atmosphere due to human activity in the Arctic.

Download Full-text

Sea ice as a source of sea salt aerosol to Greenland ice cores: a model-based study

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-9417-2017 ◽

2017 ◽

Vol 17 (15) ◽

pp. 9417-9433 ◽

Cited By ~ 20

Author(s):

Rachael H. Rhodes ◽

Xin Yang ◽

Eric W. Wolff ◽

Joseph R. McConnell ◽

Markus M. Frey

Keyword(s):

Sea Ice ◽

Atmospheric Chemistry ◽

Transport Model ◽

Ice Core ◽

Ice Cores ◽

Open Ocean ◽

Sea Salt ◽

The Arctic ◽

Sea Salt Aerosol ◽

Annual Variability

Abstract. Growing evidence suggests that the sea ice surface is an important source of sea salt aerosol and this has significant implications for polar climate and atmospheric chemistry. It also suggests the potential to use ice core sea salt records as proxies for past sea ice extent. To explore this possibility in the Arctic region, we use a chemical transport model to track the emission, transport, and deposition of sea salt from both the open ocean and the sea ice, allowing us to assess the relative importance of each. Our results confirm the importance of sea ice sea salt (SISS) to the winter Arctic aerosol burden. For the first time, we explicitly simulate the sea salt concentrations of Greenland snow, achieving values within a factor of two of Greenland ice core records. Our simulations suggest that SISS contributes to the winter maxima in sea salt characteristic of ice cores across Greenland. However, a north–south gradient in the contribution of SISS relative to open-ocean sea salt (OOSS) exists across Greenland, with 50 % of winter sea salt being SISS at northern sites such as NEEM (77° N), while only 10 % of winter sea salt is SISS at southern locations such as ACT10C (66° N). Our model shows some skill at reproducing the inter-annual variability in sea salt concentrations for 1991–1999, particularly at Summit where up to 62 % of the variability is explained. Future work will involve constraining what is driving this inter-annual variability and operating the model under different palaeoclimatic conditions.

Download Full-text

Sea ice as a source of sea salt aerosol to Greenland ice cores: a model-based study

10.5194/acp-2017-100 ◽

2017 ◽

Cited By ~ 1

Author(s):

Rachael H. Rhodes ◽

Xin Yang ◽

Eric W. Wolff ◽

Joseph R. McConnell ◽

Markus M. Frey

Keyword(s):

Sea Ice ◽

Atmospheric Chemistry ◽

Transport Model ◽

Ice Core ◽

Ice Cores ◽

Open Ocean ◽

Sea Salt ◽

The Arctic ◽

Sea Salt Aerosol ◽

Annual Variability

Abstract. Growing evidence suggests that the sea ice surface is an important source of sea salt aerosol and this has significant implications for polar climate and atmospheric chemistry. It also offers the opportunity to use ice core sea salt records as proxies for past sea ice extent. To explore this possibility in the Arctic region, we use a chemical transport model to track the emission, transport and deposition of sea salt from both the open ocean and the sea ice, allowing us to assess the relative importance of each. Our results confirm the importance of sea ice sea salt (SISS) to the winter Arctic aerosol burden. For the first time, we explicitly simulate the sea salt concentrations of Greenland snow and find they match high resolution Greenland ice core records to within a factor of two. Our simulations suggest that SISS contributes to the winter maxima in sea salt characteristic of ice cores across Greenland. A north-south gradient in the contribution of SISS relative to open ocean sea salt (OOSS) exists across Greenland, with 50 % of sea salt being SISS at northern sites such as NEEM, while only 10 % of sea salt is SISS at southern locations such as ACT10C. Our model shows some skill at reproducing the inter-annual variability in sea salt concentrations for 1991–1999 AD, particularly at Summit where up to 62 % of the variability is explained. Future work will involve constraining what is driving this inter-annual variability and operating the model under different paleoclimatic conditions.

Download Full-text

Exploring ice core sea ice proxies through process-based modelling

10.5194/egusphere-egu21-16037 ◽

2021 ◽

Author(s):

Rachael Rhodes ◽

Xin Yang ◽

Eric Wolff

Keyword(s):

Sea Ice ◽

Atmospheric Chemistry ◽

Transport Model ◽

Ice Core ◽

Ice Cores ◽

Internal Variability ◽

Atmospheric Composition ◽

Chemical Transport Model ◽

Aerosol Emission ◽

Abrupt Shifts

It is important to understand the magnitude and rate of past sea ice changes, as well as their timing relative to abrupt shifts in other components of Earth&#8217;s climate system. Furthermore, records of past sea ice over the last few centuries are urgently needed to assess the scale of natural (internal) variability over decadal timescales. By continuously recording past atmospheric composition, polar ice cores have the potential to document changing sea ice conditions if atmospheric chemistry is altered.&#160; Sea salt aerosol, specifically sodium (Na), and bromine enrichment (Brenr, Br/Na enriched relative to seawater ratio) are two ice core sea ice proxies suggested following this premise.Here we aim to move beyond a conceptual understanding of the controls on Na and Brenr in ice cores by using process-based modelling to test hypotheses. We present results of experiments using a 3D global chemical transport model (p-TOMCAT) that represents marine aerosol emission, transport and deposition. Critically, the complex atmospheric chemistry of bromine is also included allowing us to explore the partitioning of Br between gas and aerosol phases. &#160;

Download Full-text

A reinterpretation of sea-salt records in Greenland and Antarctic ice cores?

Annals of Glaciology ◽

10.3189/172756404781814681 ◽

2004 ◽

Vol 39 ◽

pp. 276-282 ◽

Cited By ~ 16

Author(s):

Andrew M. Rankin ◽

Eric W. Wolff ◽

Robert Mulvaney

Keyword(s):

Sea Ice ◽

Ice Core ◽

Open Water ◽

Weddell Sea ◽

Sea Salt ◽

Sea Salt Aerosol ◽

Ice Surface ◽

Frost Flowers ◽

Ice Production ◽

Ice Core Records

AbstractIt has recently been shown that much sea-salt aerosol around the coast of Antarctica is generated not from open water, but from the surface of newly formed sea ice. Previous interpretations of ice-core records have disregarded the sea-ice surface as a source of sea salt. The majority of sea-salt aerosol at Halley research station originates from frost flowers rather than open water, and the seasonal cycle of sea salt in aerosol at Halley appears to be controlled by ice production in the Weddell Sea, as well as variations in wind speed. Frost flowers are also an important source of aerosol at Siple Dome, suggesting that variations in sea-salt concentrations in the core, and other cores drilled in similar locations, may be reflecting changes in sea-ice production rather than changes in transportation patterns. For Greenland cores, and those from low-accumulation inland sites in Antarctica, it is not simple to calculate the proportion of sea salt originating from frost flowers rather than open water. However, modelling studies suggest that a sea-ice surface source contributed much of the flux of sea salt to these sites in glacial periods, suggesting that interpretations of ice-core records from these locations should also be revisited.

Download Full-text

Supplementary material to "Sea ice as a source of sea salt aerosol to Greenland ice cores: a model-based study"

10.5194/acp-2017-100-supplement ◽

2017 ◽

Author(s):

Rachael H. Rhodes ◽

Xin Yang ◽

Eric W. Wolff ◽

Joseph R. McConnell ◽

Markus M. Frey

Keyword(s):

Sea Ice ◽

Ice Cores ◽

Sea Salt ◽

Sea Salt Aerosol ◽

Model Based ◽

Supplementary Material

Download Full-text

The effect of sea ice loss on sea salt aerosol concentrations and the radiative balance in the Arctic

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-28859-2010 ◽

2010 ◽

Vol 10 (11) ◽

pp. 28859-28908 ◽

Cited By ~ 1

Author(s):

H. Struthers ◽

A. M. L. Ekman ◽

P. Glantz ◽

T. Iversen ◽

A. Kirkevåg ◽

...

Keyword(s):

Sea Ice ◽

Sea Salt ◽

The Arctic ◽

Polar Cap ◽

Sea Ice Extent ◽

Arctic Clouds ◽

Radiative Balance ◽

Sea Salt Aerosol ◽

Aerosol Emissions ◽

Natural Aerosol

Abstract. Understanding Arctic climate change requires knowledge of both the external and the local drivers of Arctic climate as well as local feedbacks within the system. An Arctic feedback mechanism relating changes in sea ice extent to an alteration of the emission of sea salt aerosol and the consequent change in radiative balance is examined. A set of idealized climate model simulations were performed to quantify the radiative effects of changes in sea salt aerosol emissions induced by prescribed changes in sea ice extent. The model was forced using sea ice concentrations consistent with present day conditions and projections of sea ice extent for 2100. Sea salt aerosol emissions increase in response to a decrease in sea ice, the model results showing an annual average increase in number emission over the polar cap (70–90° N) of 86×106 m−2 s−1 (mass emission increase of 23 μg m−2 s−1). This in turn leads to an increase in the natural aerosol optical depth of approximately 23%. In response to changes in aerosol optical depth, the natural component of the aerosol direct forcing over the Arctic polar cap is estimated to be between −0.2 and −0.4 W m−2 for the summer months, which results in a negative feedback on the system. The model predicts that the change in first indirect aerosol effect (cloud albedo effect) is approximately a factor of ten greater than the change in direct aerosol forcing although this result is highly uncertain due to the crude representation of Arctic clouds and aerosol-cloud interactions in the model. This study shows that both the natural aerosol direct and first indirect effects are strongly dependent on the surface albedo, highlighting the strong coupling between sea ice, aerosols, Arctic clouds and their radiative effects.

Download Full-text

Evaluating the impact of blowing-snow sea salt aerosol on springtime BrO and O3 in the Arctic

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-7335-2020 ◽

2020 ◽

Vol 20 (12) ◽

pp. 7335-7358 ◽

Cited By ~ 1

Author(s):

Jiayue Huang ◽

Lyatt Jaeglé ◽

Qianjie Chen ◽

Becky Alexander ◽

Tomás Sherwen ◽

...

Keyword(s):

Sea Ice ◽

Sea Salt ◽

The Arctic ◽

Blowing Snow ◽

Sea Salt Aerosol ◽

Surface Sites ◽

Surface Snow ◽

Ozone Monitoring ◽

Halogen Activation ◽

Arctic Surface

Abstract. We use the GEOS-Chem chemical transport model to examine the influence of bromine release from blowing-snow sea salt aerosol (SSA) on springtime bromine activation and O3 depletion events (ODEs) in the Arctic lower troposphere. We evaluate our simulation against observations of tropospheric BrO vertical column densities (VCDtropo) from the GOME-2 (second Global Ozone Monitoring Experiment) and Ozone Monitoring Instrument (OMI) spaceborne instruments for 3 years (2007–2009), as well as against surface observations of O3. We conduct a simulation with blowing-snow SSA emissions from first-year sea ice (FYI; with a surface snow salinity of 0.1 psu) and multi-year sea ice (MYI; with a surface snow salinity of 0.05 psu), assuming a factor of 5 bromide enrichment of surface snow relative to seawater. This simulation captures the magnitude of observed March–April GOME-2 and OMI VCDtropo to within 17 %, as well as their spatiotemporal variability (r=0.76–0.85). Many of the large-scale bromine explosions are successfully reproduced, with the exception of events in May, which are absent or systematically underpredicted in the model. If we assume a lower salinity on MYI (0.01 psu), some of the bromine explosions events observed over MYI are not captured, suggesting that blowing snow over MYI is an important source of bromine activation. We find that the modeled atmospheric deposition onto snow-covered sea ice becomes highly enriched in bromide, increasing from enrichment factors of ∼5 in September–February to 10–60 in May, consistent with composition observations of freshly fallen snow. We propose that this progressive enrichment in deposition could enable blowing-snow-induced halogen activation to propagate into May and might explain our late-spring underestimate in VCDtropo. We estimate that the atmospheric deposition of SSA could increase snow salinity by up to 0.04 psu between February and April, which could be an important source of salinity for surface snow on MYI as well as FYI covered by deep snowpack. Inclusion of halogen release from blowing-snow SSA in our simulations decreases monthly mean Arctic surface O3 by 4–8 ppbv (15 %–30 %) in March and 8–14 ppbv (30 %–40 %) in April. We reproduce a transport event of depleted O3 Arctic air down to 40∘ N observed at many sub-Arctic surface sites in early April 2007. While our simulation captures 25 %–40 % of the ODEs observed at coastal Arctic surface sites, it underestimates the magnitude of many of these events and entirely misses 60 %–75 % of ODEs. This difficulty in reproducing observed surface ODEs could be related to the coarse horizontal resolution of the model, the known biases in simulating Arctic boundary layer exchange processes, the lack of detailed chlorine chemistry, and/or the fact that we did not include direct halogen activation by snowpack chemistry.

Download Full-text

Greenland during the last interglacial: the relative importance of insolation and oceanic changes

Climate of the Past ◽

10.5194/cp-12-1907-2016 ◽

2016 ◽

Vol 12 (9) ◽

pp. 1907-1918 ◽

Cited By ~ 3

Author(s):

Rasmus A. Pedersen ◽

Peter L. Langen ◽

Bo M. Vinther

Keyword(s):

Sea Ice ◽

General Circulation ◽

Ice Core ◽

Ice Sheet ◽

Circulation Model ◽

The Arctic ◽

Interglacial Period ◽

Last Interglacial ◽

Ice Core Record ◽

The Impact

Abstract. Insolation changes during the Eemian (the last interglacial period, 129 000–116 000 years before present) resulted in warmer than present conditions in the Arctic region. The NEEM ice core record suggests warming of 8 ± 4 K in northwestern Greenland based on stable water isotopes. Here we use general circulation model experiments to investigate the causes of the Eemian warming in Greenland. Simulations of the atmospheric response to combinations of Eemian insolation and preindustrial oceanic conditions and vice versa are used to disentangle the impacts of the insolation change and the related changes in sea surface temperatures and sea ice conditions. The changed oceanic conditions cause warming throughout the year, prolonging the impact of the summertime insolation increase. Consequently, the oceanic conditions cause an annual mean warming of 2 K at the NEEM site, whereas the insolation alone causes an insignificant change. Taking the precipitation changes into account, however, the insolation and oceanic changes cause more comparable increases in the precipitation-weighted temperature, implying that both contributions are important for the ice core record at the NEEM site. The simulated Eemian precipitation-weighted warming of 2.4 K at the NEEM site is low compared to the ice core reconstruction, partially due to missing feedbacks related to ice sheet changes and an extensive sea ice cover. Surface mass balance calculations with an energy balance model further indicate that the combination of temperature and precipitation anomalies leads to potential mass loss in the north and southwestern parts of the ice sheet. The oceanic conditions favor increased accumulation in the southeast, while the insolation appears to be the dominant cause of the expected ice sheet reduction. Consequently, the Eemian is not a suitable analogue for future ice sheet changes.

Download Full-text