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gfdl's home page > gfdl on-line bibliography > 2002: Deep-Sea Research, Part II, 49(1-3), 345-362
Possible biological or physical explanations for decadal scale trends in North Pacific nutrient concentrations and oxygen utilization
| Keller, K., R. D. Slater, M. Bender, and R. M. Key, 2002: Possible biological or physical explanations for decadal scale trends in North Pacific nutrient concentrations and oxygen utilization. Deep-Sea Research, Part II, 49(1-3), 345-362. |
Abstract: We analyze North Pacific GEOSECS (1970s)
and WOCE (1990s) observations to examine potential decadal trends of
the marine biological carbon pump. Nitrate concentrations
([NO3]) and apparent oxygen
utilization (AOU) decreased significantly in intermediate waters
(by -0.6 and -2.9 μmol kg-1,
respectively, at
= 27.4 kg m-3, corresponding to
 1050 m).
In shallow waters (above roughly 750 m) [NO3]
and AOU increased, though the changes were not statistically significant.
A sensitivity study with an ocean general circulation model indicates
that reasonable perturbations of the biological carbon pump due to
changes in export production or remineralization efficiency are
insufficient to account for the intermediate water tracer trends.
However, changes in water ventilation rates could explain the
intermediate water tracer trends and would be consistent with trends
of water age derived from radiocarbon. Trends in AOU and
[NO3] provide relatively poor
constraints on decadal scale trends in the marine biological carbon
pump for two reasons. First, most of the expected changes due to
decadal scale perturbations of the marine biota occur in shallow waters,
where the available data are typically too sparse to account for the
strong spatial and temporal variability. Second, alternative explanations
for the observed tracer trends (e.g., changes in the water ventilation rates)
cannot be firmly rejected. Our data analysis does not disprove the
null-hypothesis of an unchanged biological carbon pump in the North Pacific. |