Open AccessEuphotic zone variations in bulk and compound‐specific δ 13 C of suspended organic matter in the Subantarctic Ocean, south of Australia
Author(s) -
O'Leary T.,
Trull T. W.,
Griffiths F. B.,
Tilbrook B.,
Revill A. T.
Publication year - 2001
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2000jc000288
Subject(s) - photic zone , mixed layer , remineralisation , organic matter , dissolved organic carbon , geology , total organic carbon , oceanography , sedimentary rock , growth rate , mineralogy , phytoplankton , chemistry , environmental chemistry , paleontology , nutrient , inorganic chemistry , geometry , mathematics , organic chemistry , fluoride
The carbon isotopic compositions of suspended organic matter δ 13 C POC collected from Subantarctic Zone surface waters south of Australia in November 1995 decrease southward from −20 to −26‰ and display strong correlations with aqueous carbon dioxide concentration ([CO 2 ]aq), consistent with previous studies. In contrast, vertical profiles through the euphotic zone (top ∼100 m) of δ 13 C POC at six stations display decreases with depth of up to 2.4‰. These decreases in δ 13 C POC cannot be fully explained by the small vertical variations in [CO 2 ]aq or its 13 C content. Carbon 13 analyses of several individual sterols revealed similar isotopic changes with depth, suggesting that they derive from a fundamental depth control on primary production, rather than from algal community variations or remineralization processes. Growth rate μ appears to be the most likely source of the depth variations. The relationship between μ/[CO 2 ]aq and δ 13 C POC derived from surface water samples can explain the vertical variations of δ 13 C POC within the mixed layer, provided integrated mixed layer growth rates are used. Below the mixed layer, differences between the observed δ 13 C POC and the growth rate model can be explained by recent shallowing in mixed layer depth and the subsequent effect on growth rates. These results suggest that δ 13 C POC determinations can be used to provide some information on the recent history of mixed layer processes and that interpretation of sedimentary δ 13 C POC records should include consideration of possible growth rate and mixed layer depth variations.