Comparison of surface radiative flux data sets over the Arctic Ocean

Abstract. In addition to scattering coefficients, the light absorption coefficients of particulate and dissolved materials are the main factors determining the light propagation of the visible part of the spectrum and are, thus, important for developing ocean color algorithms. While these absorption properties have recently been documented by a few studies for the Arctic Ocean (e.g., Matsuoka et al., 2007, 2011; Ben Mustapha et al., 2012), the data sets used in the literature were sparse and individually insufficient to draw a general view of the basin-wide spatial and temporal variations in absorption. To achieve such a task, we built a large absorption database of the Arctic Ocean by pooling the majority of published data sets and merging new data sets. Our results show that the total nonwater absorption coefficients measured in the eastern Arctic Ocean (EAO; Siberian side) are significantly higher than in the western Arctic Ocean (WAO; North American side). This higher absorption is explained by higher concentration of colored dissolved organic matter (CDOM) in watersheds on the Siberian side, which contains a large amount of dissolved organic carbon (DOC) compared to waters off North America. In contrast, the relationship between the phytoplankton absorption (a&varphi;(λ)) and chlorophyll a (chl a) concentration in the EAO was not significantly different from that in the WAO. Because our semianalytical CDOM absorption algorithm is based on chl a-specific a&varphi;(λ) values (Matsuoka et al., 2013), this result indirectly suggests that CDOM absorption can be appropriately derived not only for the WAO but also for the EAO using ocean color data. Based on statistics, derived CDOM absorption values were reasonable compared to in situ measurements. By combining this algorithm with empirical DOC versus CDOM relationships, a semianalytical algorithm for estimating DOC concentrations for river-influenced coastal waters of the Arctic Ocean is presented and applied to satellite ocean color data.

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A changing Arctic Ocean: How measured and modeled 129I distributions indicate fundamental shifts in circulation between 1994 and 2015

10.5194/egusphere-egu21-7198 ◽

2021 ◽

Author(s):

Michael J. Karcher ◽

John N. Smith ◽

Núria Casacuberta ◽

William J. Williams ◽

Tim Kenna ◽

...

Keyword(s):

Arctic Ocean ◽

Ocean Circulation ◽

Large Scale ◽

The Arctic ◽

Strong Increase ◽

Climate Indices ◽

Data Sets ◽

Boundary Current ◽

The Arctic Ocean ◽

Atlantic Origin

129I measurements on samples collected during GEOTRACES oceanographic missions in the Arctic Ocean in 2015 have provided the first detailed, synoptic 129I sections across the Eurasian, Canada and Makarov Basins. 129I is discharged from European nuclear fuel reprocessing plants since several decades and is carried north into the Arctic Ocean with waters of Atlantic origin. Here the measurements of its passage can be used to identify the ocean circulation at different depth horizons. Elevated 129I levels measured over the Lomonosov and Alpha-Mendeleyev Ridges in 2015 were associated with tracer labeled, Atlantic-origin water bathymetrically steered by the ridge systems through the central Arctic while lower 129I levels were evident in the more poorly ventilated basin interiors. 129I levels of 200-400 x 107 at/l measured in intermediate waters had increased by a factor of 10 compared to results from the same locations in 1994-1996 owing to the arrival of a strong increase in the discharges from La Hague, that occurred during the 1990s. Comparisons of the patterns of 129I between the mid-1990s and 2015 delineate large scale circulation changes that occurred during the shift from a positive Arctic Oscillation and a cyclonic circulation regime in the mid-1990s to anticyclonic circulation in 2015. These are characterized by a broadened Beaufort Gyre in the upper ocean, a weakened boundary current and partial AW flow reversal in the southern Canada Basin at mid-depth. Tracer 129I simulations using the coupled ocean-sea ice model NAOSIM agree with both, the historical 129I results and recent GEOTRACES data sets, thereby lending context and credibility to the interpretation of large-scale changes in Arctic circulation and their relationship to shifts in climate indices revealed by the tracer 129I distributions. We will present measurements and simulation results of 129I for the 1990s and 2015 and put them into the context of ocean circulation responses to changing atmospheric forcing regimes.

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