2:00 PM - 2:15 PM
[ACG46-07] Recent increase in DMS emission from seasonal sea ice area inferred from a high-time-resolution Greenland ice core
Keywords:methane sulfonic acid, ice core, phytoplankton, dimethyl sulfide, sea ice retreat
Dimethyl sulfide (DMS), which originated from ocean phytoplankton, is oxidized to sulfate and methane sulfonic acid (MSA) after emission into the atmosphere. These aerosols contribute to the formation of cloud condensation nuclei in the marine atmosphere and participate in negative cloud radiative forcing. Model studies suggest that declines in Arctic sea ice may lead to increased DMS emissions. To estimate the increase in DMS emissions associated with future sea ice reduction and its impacts on the cloud radiative forcing, extensive and long-term aerosol monitoring are needed. However, there is little long-term continuous monitoring data for aerosol MSA and oceanic DMS in the pan-Arctic, and the long-term variations of DMS emission from observations are not revealed. The objective of this study is to reveal the variations of phytoplankton bloom and oceanic DMS emissions over 55 years using the Greenland ice core drilled at a high accumulation area, where atmospheric aerosols are preserved with high precision.
We analyzed a 90.45 m depth ice core drilled at the southeastern dome of the Greenland Ice Sheet (SE-Dome; 67.18°N, 36.37°W, 3170m above sea level) in 2015. For analyses of chemical species in the ice core, we divided the ice core into 100 mm depth sections in a cold room. The samples were decontaminated using a clean ceramic knife in a cold clean room, put into a cleaned polyethylene bottle, and then melted in the bottle at room temperature in a clean room. The methane-sulfonate ion (MS-) was measured by ion chromatography (Thermo Scientific, ICS-2100). We used a Dionex AS-14A column with 23mM KOH gradient eluent for MS- (we describe MS- as MSA). The SE-Dome ice core was dated based on pattern matching of the oxygen isotope variations between the ice core record and a simulated profile. The number of samples was 395 from 1960 to 2014, corresponding to 7 samples per year on average.
The interannual trend of the annual flux of MSA (MSAflux) substantially decreased from 1960 to 2001 and remarkably increased after 2002. The seasonal variation of MSAflux showed a single peak of spring in 1960-2001 and a bimodal pattern with peaks of spring and summer in 2002-2014. The spring MSAflux highly correlated with the chlorophyll-a (Chl-a) concentration in the Irminger sea (r = 0.69, p < 0.01). The summer MSAflux in 2002-2014 was 3-6 times higher than that in 1972-2001. Satellite data showed that the sea ice along southeastern coast of Greenland after 2002 had retreated in July, when the sea surface photosynthetically active radiation was high, and the Chl-a concentrations increased significantly in the same area. The increased summer MSAflux in 2002-2014 results from the early retreat of the sea ice followed by an increase in DMS emission from enhanced phytoplankton production. We propose that the oceanic DMS emission in the pan-Arctic has remarkably increased in summer since the early 2000s due to the early retreat of sea ice.
We analyzed a 90.45 m depth ice core drilled at the southeastern dome of the Greenland Ice Sheet (SE-Dome; 67.18°N, 36.37°W, 3170m above sea level) in 2015. For analyses of chemical species in the ice core, we divided the ice core into 100 mm depth sections in a cold room. The samples were decontaminated using a clean ceramic knife in a cold clean room, put into a cleaned polyethylene bottle, and then melted in the bottle at room temperature in a clean room. The methane-sulfonate ion (MS-) was measured by ion chromatography (Thermo Scientific, ICS-2100). We used a Dionex AS-14A column with 23mM KOH gradient eluent for MS- (we describe MS- as MSA). The SE-Dome ice core was dated based on pattern matching of the oxygen isotope variations between the ice core record and a simulated profile. The number of samples was 395 from 1960 to 2014, corresponding to 7 samples per year on average.
The interannual trend of the annual flux of MSA (MSAflux) substantially decreased from 1960 to 2001 and remarkably increased after 2002. The seasonal variation of MSAflux showed a single peak of spring in 1960-2001 and a bimodal pattern with peaks of spring and summer in 2002-2014. The spring MSAflux highly correlated with the chlorophyll-a (Chl-a) concentration in the Irminger sea (r = 0.69, p < 0.01). The summer MSAflux in 2002-2014 was 3-6 times higher than that in 1972-2001. Satellite data showed that the sea ice along southeastern coast of Greenland after 2002 had retreated in July, when the sea surface photosynthetically active radiation was high, and the Chl-a concentrations increased significantly in the same area. The increased summer MSAflux in 2002-2014 results from the early retreat of the sea ice followed by an increase in DMS emission from enhanced phytoplankton production. We propose that the oceanic DMS emission in the pan-Arctic has remarkably increased in summer since the early 2000s due to the early retreat of sea ice.