5:15 PM - 6:45 PM
[ACG42-P12] Influence of the Alaska Coastal Current on depositional process of organic matter in Barrow Canyon
Keywords:Barrow Canyon , Mackenzie Trough, palynofacies, amorphous organic matter
The Arctic Ocean has been significantly impacted by recent and rapid climate change. The IPCC has emphasized of revealing the environmental changes occurring in this region. As is well known, observable changes have occurred in both marine and terrestrial environments in the Arctic Ocean. Barrow Canyon is known for its high productivity due to upwelling and for higher sedimentation rates caused by the Alaskan Coastal Current. The Alaska Coastal Current is an ocean current that flows from the North Pacific Ocean through the Bering Strait into the Arctic Ocean, at depths of ~100 m depth along the Beaufort Shelf with high velocity. This current is also known as the Western Arctic Shelfbreak Current (Von Appen and Pickart, 2012). The velocity of the Shelfbreak Current is influenced by the flow through the Bering Strait (Shimada, 2011), which is possibly associated with the strengthening of the Beaufort Gyre and the decrease in summer sea ice extent (Gong and Pickart, 2015). However, the impact of the Shelfbreak Current on the depositional process of organic matter in Barrow Canyon remains uncertain. Kerogen is insoluble organic matter with organic solvent, acid and base, and divided into amorphous organic matter (AOM) and structural organic matter (SOM, including palynomorph and palynodebris). Composition from microscopic observation of kerogen is called palynofacies analysis. In this study, we performed palynofacies analysis of the sediment core from the BC2 site in Barrow Canyon, collected by FY2022 R/V Mirai Arctic Cruise as the HAPPI (Holocene Arctic Palaeoclimatology and Palaeoceanography Investigation) project, to focus on the variation in depositional process of organic matter due to rapid climate change in Anthropocene.
AOM accounts for 95% of the kerogen separated from sediment samples at the BC2 site. AOM is classified as NFA (non-fluorescent AOM), FA (fluorescent AOM) and WFA (weakly fluorescent AOM) by autofluorescence for UV with a fluorescence microscope, and is derived from wood fragments, palynomorph/cuticle fragments, and aquatic organisms, respectively (Sawada et al., 2012). In the surface sediments, despite marine sediments, NFA, FA, and WFA account for ~60%, ~20%, and ~5%, respectively, suggesting that the kerogen is mainly composed of terrigenous organic matter. Main component of SOM are cuticle fragments of terrestrial plant with fluorescent, which suggests that FA in the samples are also derived from cuticle tissue. In addition, the relative abundance of FA increased ~10% with the decrease of NFA from 1980 to 2000. These data suggest that FA-rich terrestrial organic matter deposited at the shelf edge was readily resuspended by the enhanced flow of the Shelfbreak Current due to the rapid climate change that caused the decline in summer sea ice extent from 1980 to 2000. In the future, the strengthening of the Alaska Coastal Current is expected to increase FA deposition at Barrow Cannon. This evidence supports the selective preservation and uneven distribution of AOM in the marine environment, which applies to studies of the benthic community and underground resources.
AOM accounts for 95% of the kerogen separated from sediment samples at the BC2 site. AOM is classified as NFA (non-fluorescent AOM), FA (fluorescent AOM) and WFA (weakly fluorescent AOM) by autofluorescence for UV with a fluorescence microscope, and is derived from wood fragments, palynomorph/cuticle fragments, and aquatic organisms, respectively (Sawada et al., 2012). In the surface sediments, despite marine sediments, NFA, FA, and WFA account for ~60%, ~20%, and ~5%, respectively, suggesting that the kerogen is mainly composed of terrigenous organic matter. Main component of SOM are cuticle fragments of terrestrial plant with fluorescent, which suggests that FA in the samples are also derived from cuticle tissue. In addition, the relative abundance of FA increased ~10% with the decrease of NFA from 1980 to 2000. These data suggest that FA-rich terrestrial organic matter deposited at the shelf edge was readily resuspended by the enhanced flow of the Shelfbreak Current due to the rapid climate change that caused the decline in summer sea ice extent from 1980 to 2000. In the future, the strengthening of the Alaska Coastal Current is expected to increase FA deposition at Barrow Cannon. This evidence supports the selective preservation and uneven distribution of AOM in the marine environment, which applies to studies of the benthic community and underground resources.