Contrasting sources of dissolved and particulate organic matter along 62N-72N in the Siberian-Arctic Lena River

• The Lena River transports large amounts of sediment and dissolved organic matter to the shallow Laptev Sea, where it may be subject to degradation and potential release of OC. We studied organic matter collected in summer 2008, along a 1450 km section of the Lena River, from near Yakutsk at 62°N to the deltaic region at 72°N, to better understand potential in-river processing of the terrestrial particulate and dissolved fractions in the river surface water.Carbon isotopes (δ13C and Δ14C) and plant wax lipid markers combine to reveal two distinct OC pools with different behavior in the river. The molar OC/TN ratios for POC were low (6-13) which suggests contribution from (freshwater) plankton, but most of the POC was of old age (770-4500 14C years) which rather suggests a pre-aged origin - perhaps from erosion of riverbank permafrost material. Much in contrast, COC was young (20-440 14C years) and displayed a high OC/TN composition (23-56) with a steady δ13C signal along the river course (-26.7 to -27.7). There was an apparent absence of ice complex deposit permafrost (mineral soil/yedoma OC) in the COC fraction, and only small contributions to POC. The COC signal suggest contribution from contemporary plant detritus/surface soil OC. It seems as if pre-aged permafrost OC, potentially from riverbank erosion, partitions into the particulate pool and almost not at all to the DOC/COC pool.Degradation markers indicate a highly degraded COC lipid pool and a less degraded POC - the n-alkane carbon preference index (CPI, C24-C34) was 1.0-1.3 for COC and 1.2-4.9 (on average 3.3) for POC.Taken together DOC/COC and POC have clearly different terrestrial sources and different fates on its way to the shelf waters. Previously freeze-locked old permafrost OC remobilizes into the Lena River in particulate form which (at least temporarily) escapes degradation as it follows the river course seawards in a less degraded state.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

organic carbon

stabel carbon

radiocarbon

isotopes

Lena River

colloidal matter

particulate matter

Applied Environmental Science

tillämpad miljövetenskap

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)