Am. Waite et Sd. Nodder, The effect of in situ iron addition on the sinking rates and export flux of Southern Ocean diatoms, DEEP-SEA II, 48(11-12), 2001, pp. 2635-2654
Citations number
65
Categorie Soggetti
Aquatic Sciences","Earth Sciences
Journal title
DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY
During the Southern Ocean Iron RElease Experiment (SOIREE), conducted in Fe
bruary 1999 at 61 degreesS, 141 degreesE in high nutrient, low chlorophyll
waters south of the Polar Front, we measured the intrinsic sinking rates of
diatoms at two depths inside and outside of an iron-fertilised patch. Over
all, the sinking rates of the diatoms estimated by the SETCOL method (Bienf
ang, Canadian Journal of Fisheries and Aquatic Sciences 38 (1981) 1289-1294
) were significantly lower inside than outside the patch, and a time series
of sinking rates (chlorophyll-based) indicated that the rates of cells > 2
2 mum reduced to a minimum (0.47 m d(-1)) s days after the first in situ ir
on addition. A subsequent increase in sinking rates (chlorophyll-based) of
> 22-mum cells coincided with an increase in algal iron stress (based on di
atom flavodoxin levels). The primary bloom species, Fragilariopsis kerguele
nsis and Nitzschia and Navicula sp. reduced their sinking rates most marked
ly within the patch, showing a decrease of up to 87% of initial rates, over
the 13 days of the time series. In contrast, the very largest cells( > 1 m
m, Trichotoxon and Thalassiothrix) showed little change in sinking rate ins
ide or outside the patch. Sinking rates of resident cells associated with a
deep chlorophyll maximum (40-75 m) in and out of the patch also showed no
significant sinking rate change upon iron addition. Given these results and
the known longevity of the SOIREE bloom (at least 60d), we infer that sink
ing rate reduction is an integral part of a species-specific bloom response
to elevated Fe supply. We calculate that sinking losses of iron-saturated,
unaggregated cells would have been similar to 1% d(-1). A 1% daily loss wo
uld have halved cell accumulation at the surface over 60d, primarily via a
reduction in growth potential. (C) 2001 Elsevier Science Ltd. Ah rights res
erved.