Abstract
With the Arctic warming, terrestrial input plays a more important role in carbon cycle in the Arctic Ocean than before. Chromophoric dissolved organic matter (CDOM) as a tracer of terrestrial dissolved organic matter (tDOM) becomes more valuable in elucidating the source and compositions of DOM. Although measurements of DOM in the Arctic Ocean have been widely reported, characteristics of high molecular weight colloids are still poorly understood. In this study, the bulk absorbance and size fracto- grams of CDOM were measured in the Chukchi Seas using an asymmetrical flow field-flow fractionation (AF4) coupled online with UV-vis detectors. Both CDOM a254, absorption coefficient at 254 nm, and the inte- grated UV254 (from AF4 UV-vis detector) of three colloidal fractions (1–10, 10–100, and >100 kDa) signifi- cantly correlated with the fraction of meteoric water (fmw) calculated from d18O in seawater, which indicates that the CDOM was mainly derived from terrestrial input and a254 is a potential tracer of tDOM in the Chuk- chi Sea. Compared with the larger colloidal fractions (10–100 and >100 kDa), the smaller colloidal fraction (1–10 kDa) showed a stronger correlation with the fmw, suggesting the smaller colloids were of mostly ter- rigenous origin. Values of field measured spectral slope at 275–295 nm (s275–295), a tDOM proxy, were signif- icantly lower than the model-estimated s275–295 calculated from the MODIS Aqu satellite remote sensing data, which indicated that terrestrial input of CDOM derived from model calculation was likely underesti- mated in the Chukchi Sea.