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Evaluation of the collection efficiency of upper ocean sub‐photic‐layer sediment traps: a 24‐month in situ calibration in the open Baltic Sea using 234 Th
Author(s) -
Gustafsson Örjan,
Andersson Per,
Roos Per,
Kukulska Zofia,
Broman Dag,
Larsson Ulf,
Hajdu Susanna,
Ingri Johan
Publication year - 2004
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2004.2.62
Subject(s) - settling , sediment trap , biogeochemical cycle , sediment , oceanography , environmental science , photic zone , particle (ecology) , water column , range (aeronautics) , geology , atmospheric sciences , chemistry , geomorphology , phytoplankton , environmental chemistry , nutrient , materials science , environmental engineering , composite material , organic chemistry
The collection efficiency of cylindrical sediment traps of common design was assessed in situ for more than 2 y in an offshore shelf regime using the 234 Th proxy and simultaneously collected hydrological and biogeochemical parameters. The traps were found to systematically record an undertrapping bias of 234 Th by, on average, a factor of three (range 0.8 to 10). Seasonal variations in trapping efficiency were related to the seasonally varying ballasting properties of the settling particle pool. Sediment trap 234 Th fluxes agreed within a factor of two of the estimated 234 Th export from the overlying surface waters in the winter‐spring periods in both 1999 and 2000 and appeared related to a particle pool that included, presumably rapidly sinking, mineral particles and diatom tests acting as ballast. In contrast, discrimination against slowly settling organic‐rich aggregates of apparent exudate origin resulted in undertrapping of 234 Th by factors of three to ten throughout the summerfall seasons. These data are consistent with hydrodynamic predictions that the collection efficiency of sinking particles is inversely related to their intrinsic settling velocities. Recognition of changing particle composition along a settling velocity spectrum combine with carbon mass balance restrictions to suggest that these 234 Th‐based collection efficiencies, ranging from 0.1 to 1, may not be directly applicable to “correct” sediment trap fluxes of other components, such as organic carbon. However, the 234 Th‐derived insights of settling‐velocity‐related undertrapping may beneficially be taken into account when interpreting trap records both in studies of biogeochemical element fluxes and in phytoplankton ecology.