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Variability in the O 2 /N 2 ratio of southern hemisphere air, 1991–1994: Implications for the carbon cycle
Author(s) -
Bender Michael,
Ellis Taylor,
Tans Pieter,
Francey Roger,
Lowe David
Publication year - 1996
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/95gb03295
Subject(s) - thermocline , southern hemisphere , sink (geography) , environmental science , latitude , atmospheric sciences , carbon sink , northern hemisphere , climatology , oceanography , geology , climate change , geography , cartography , geodesy
We present a record of variations in the O 2 /N 2 ratio of air at 41°S latitude from 1991–1994 based on the mass spectrometric analysis of flask samples from Cape Grim, Tasmania, and Baring Head, New Zealand. Results for Cape Grim for the period from June 1991 to February 1992 are in good agreement with previously published data of Keeling and Shertz [1992]. Plotted versus time, O 2 /N 2 ratios show the expected annual cycles. O 2 /N 2 increases in austral spring and summer (caused mainly by net oceanic production) and decreases in fall and winter (caused by ventilation of the seasonal and main thermoclines). The average amplitude of the seasonal cycle implies net oceanic production of about 5 mol C m −2 yr −1 with considerable interannual variability. The O 2 /N 2 ratio of air decreased at the rate of 12±4 per meg/yr (0.012 ‰/yr) between winter 1991 and winter 1993. This value is considerably less than the O 2 consumption rate associated with fossil fuel burning (about 20 per meg/yr), suggesting that the land biosphere was an O 2 source and an important CO 2 sink during this period. Alternatively, the oceans may have been a transient O 2 sink during 1991–1993, most likely caused by an enhanced rate of thermocline ventilation with respect to the steady‐state value.