Rainer M.W. Amon1, Benedikt Meon2 Missing organic carbon in the coastal Kara Sea – Is coastal erosion a significant source? Rainer M.W. Amon1, Benedikt Meon2 1Texas A&M University at Galveston, Dept. of Marine Sciences and Oceanography, Galveston, USA 2Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

East Siberian Sea Laptev Sea Yenisei Kara Sea OB Barents Sea

Why are we interested in terrestrially- and permafrost-derived organic matter in the Arctic Coastal Ocean ? The role of terrestrially-derived organic matter as a carbon and nutrient source for the Arctic Ocean food web. The use of terrestrial organic matter as a tracer for water mass dynamics and environmental change in the Arctic Ocean.

DISTRIBUTION OF DOC ALONG THE SALINITY GRADIENT BP 99 Ob (08/24-09/07 ) y = -12,2x + 597 R 2 = 0,865 100 200 300 400 500 600 700 800 5 10 15 20 25 30 35 DOC [µM C ] BP 99 Yen (08/26-09/06) y = -18,5x + 740 R 2 = 0,949 100 200 300 400 500 600 700 800 5 10 15 20 25 30 35 BP 00 Ob (09/03-09/21) y = -16,4x + 617 R 2 = 0,903 100 200 300 400 500 600 700 800 5 10 15 20 25 30 35 salinity [psu] DOC [µM C ] BP 00 Yen (09/06-09/19) y = -18,3x + 679 R 2 = 0,948 100 200 300 400 500 600 700 800 5 10 15 20 25 30 35 salinity [psu]

RIVER DOM LOSSES ON THE SHELF A 100 200 300 400 500 600 700 5 10 15 20 25 30 35 salinity [psu] 40 DOC [µM C] POC [µM C] DOC (µM) POC (µM) Flocculation experiment:<5% losses Time [d] 2 4 6 8 600 DOC [µM] 500 550 650 700 750 Bacterial decomposition experiment: <5% losses

TERRESTRIAL-DOM EXPORT FROM THE ARCTIC OCEAN Amon et al. 2003

Bacterial activity and DOM 350 300 Surface y = 38.18x + 37.191 300 Pycnocline 250 r = 0.78 p < 0.001 250 Close to bottom 200 Leucine inc. (pM h-1) 200 Leucine inc. (pM h-1) 150 150 100 100 50 50 Ob Yenisei Estuary Kara Sea 1 2 3 4 5 (5-15 psu) (>20 psu) Chl a (µg l-1) 0.3 0.25 0.2 Tg C per day ? 0.15 0.1 0.05 Bacterial carbon demand Primary production River input

DISTRIBUTION OF TERRESTRIAL-DERIVED DOM IN THE ARCTIC OCEAN -28 No sign of increased concentrations of terrestrial DOM in the deep Fram Strait and the deep central Arctic Ocean. Unpublished data from the Laptev Sea slope and the Mendeleev Ridge indicate vertical transport of terrestrial DOM to at least 1600 m. These observations might suggest a change in deep water formation patterns over the last decade in the Arctic Ocean. rivers EGC -26 Atlantic water PDW GIN Sea -24  13C PSW -22 -20 10 100 1000 10000 100000 Lignin phenols (ng/l) 5 10 15 20 25 30 35 % TDOC Arctic SW (≤55m) Arctic DW (≥1000m) Arctic IMW (60-600m)

COMPOSITION OF RIVER UDOM Ob 97 Ob 99 Yenisei 97 Yenisei 99 C/N 43.5 39.8 48.1 42.3 δ 13C -27.6 -27.7 -27.1 15N 2.5 2.8 1.9 2.6 Δ14C 84 307 150 108 lignin 23.5 24.7 33 50 NS yield 3.1 4.1 1.8 2 Is DO14C a valuable tracer for the mobilization of Permafrost organic matter in the Arctic Ocean?

COMPOSITION OF MOLECULAR WEIGHT FRACTIONS Size fractions Neutral sugars (%OC) 10 15 20 25 30 35 40 45 50 -29 -28 -27 -26 -25 -24 Total UDOM > 100 kDa 30 - 100 kDa 1 - 30 kDa C/N 13C

CONCLUSIONS Carbon metabolism studies in the Kara Sea demonstrate our poor understanding of carbon sources and sinks on Arctic Shelves – costal erosion has not been considered as a carbon and nutrient source yet. In general, terrestrially-derived DOM from major Siberian Rivers appears conservative providing a potential tracer for water mass dynamics and environmental change for Arctic shelves and the central Arctic Ocean, at least on a 2-6 year time scale. The Eurasian and Canadian Arctic might differ. DO14C values of Siberian River DOM appear modern suggesting that at the moment there is no mobilization of old permafrost organic matter into the river DOM pool, however, partitioning and bioavailability of permafrost organic matter needs to be determined. There is some evidence that the incorporation of terrestrial-derived DOM into Arctic Ocean deep water might have changed over the last decade.

ACKNOWLEDGEMENTS Captain, scientists, and crew of Polarstern, Akademik Boris Petrov, USS Pogy, USS Archerfish, USS Hawkbill Ron Benner University of South Carolina; Funding: German Federal Ministry for Education and Research, European Community (COMET), DAAD (German Academic Exchange Service), US National Science Foundation

RELATIONSHIP BETWEEN FLUORESCENCE (350-460/550NM), RIVERINE DOM AND LIGNIN PHENOL CONCENTRATIONS y = 0.1218x + 0.3786 R 2 = 0.999 0.5 1 1.5 2.5 3 3.5 4 5 10 15 20 25 30 % river Water y = 2350.7x - 853.56 = 0.9046 50 100 150 200 250 300 350 400 450 500 0.3 0.35 0.4 0.45 0.55 0.6 Fluorescence (350-460/550nm) Fluorescence (V) LOP (µg/l) Amon et al. 2003

BIOLOGICAL AND PHYSICAL PROCESSES ON ARCTIC SHELVES 30 psu ------------------------- surface salinity ------------------------------- 0 psu ~100 µM ------------------------ surface DOC ----------------------------- ~700 µM River runoff sea ice formation PP PP PP Brine release: enrichment of salt and DOM export mixing bacterial DOM utilization Nutrient regeneration Modified shelf water