[ACG38-P17] Optical tracer method to distinguish fresh water sources in the Pacific Arctic region
Keywords:absorption of CDOM, Pacific Arctic region, fresh water sources
Recent freshening of the Arctic Ocean caused notable changes in ocean environment and circulations. Both increases in sea ice melt water and river discharge are known to have a large effect on the freshening. Chemical tracers, oxygen isotope ratio and total alkalinity (TA), are used to distinguish fresh water sources to understand their contribution to the freshening and distribution of the water masses. However, estimation of fresh water sources using chemical tracers has a disadvantage in high frequent sampling, because it takes considerable time to measure. In this study, we propose a method to discriminate water sources using absorption of CDOM (aCDOM) for the Pacific Arctic region.
We obtained salinity, TA, and aCDOM at 443 nm (aCDOM(443)) from the seven cruises of R/V Mirai conducted in the Pacific Arctic region during late summer. Fraction of sea ice melt water (fSIM) and other fresh water (fOF) were calculated from their known end-member values of salinity and TA. We identified aCDOM(443) end-member values of fSIM and fOF, which were unknown, applying a least-square method to the relationship between fresh water fraction and aCDOM(443). Thus, fSIM and fOF became retrievable from salinity and aCDOM(443) instead of TA. We also evaluated the accuracy of the optical tracer method comparing fresh water fraction values calculated from chemical and optical tracers, and obtained equivalent results to the chemical tracer method. Estimation of fresh water sources with higher frequent monitoring using aCDOM might advance the comprehension of ocean circulation and related chemical- and biological system in the Arctic.
We obtained salinity, TA, and aCDOM at 443 nm (aCDOM(443)) from the seven cruises of R/V Mirai conducted in the Pacific Arctic region during late summer. Fraction of sea ice melt water (fSIM) and other fresh water (fOF) were calculated from their known end-member values of salinity and TA. We identified aCDOM(443) end-member values of fSIM and fOF, which were unknown, applying a least-square method to the relationship between fresh water fraction and aCDOM(443). Thus, fSIM and fOF became retrievable from salinity and aCDOM(443) instead of TA. We also evaluated the accuracy of the optical tracer method comparing fresh water fraction values calculated from chemical and optical tracers, and obtained equivalent results to the chemical tracer method. Estimation of fresh water sources with higher frequent monitoring using aCDOM might advance the comprehension of ocean circulation and related chemical- and biological system in the Arctic.