Article,
Carbonate system response to iron enrichment
MARINE CHEMISTRY, 62 (1-2): 31--43 (1998)
Abstract
In May of 1995, the second iron experiment (IronEx II) was carried
out in the Equatorial Pacific Ocean (beginning at 3.5 degrees S and
104.5 degrees W) with the purpose of examining the effect of iron
enrichment in high nutrient, low chlorophyll (HNLC) waters. During
the cruise, the carbonate parameters TA (total alkalinity), TCO2
(total inorganic carbon), pH and pCO(2) (partial pressure of CO2)
were determined from water samples both inside and outside the iron-fertilized
patch. The carbonate parameters, along with hydrographic properties,
were found to be uniform in the surface waters of the study area
before the addition of iron. Values were found to be pH = 7.93 +/-
0.02, TA = 2311 +/- 5 mu mol kg(-1), TCO2 = 2051 +/- 4 mu mol kg(-1),
and pCO(2) = 538 +/- 12 mu atm. The response of the carbonate system
to an initial 2 nM iron infusion and two subsequent 1 nM reinfusions
to the surface water was measured several times a day during the
study. The maximum changes of the carbonate parameters within the
patch relative to 'outside' measurements were -27 mu mol kg(-1) in
TCO2, -73 mu atm in pCO(2), and +0.058 in pH on days 8 and 9 of the
experiment. The TA did not change within the experimental error of
the measurements +/- 3 mu mol kg(-1)). In addition to the daily measurements,
three transects were made across the patch (at 63, 78, and 122 h
post-addition) that show a spatial biochemical response to the influence
of iron and correlations between nutrients and the various carbonate
parameters. A diel study of the patch showed daytime decreases of
27 mu atm in pCO(2) and 16 mu mol kg(-1) in TCO2. The changes in
carbon to nutrients during the experiment give Delta NO3/Delta PO4
= 14.3 +/- 0.7, Delta C/Delta NO3 = 6.2 +/- 0.2, Delta C/Delta PO4
= 90 +/- 5, Delta C/Delta O-2 = -0.66 +/- 0.07, Delta C/Delta SiO2
= 5.05 +/- 0.3. Corrections for the flux of gases across the air-sea
interface during the experiment affect the oxygen changes, giving
Delta C/Delta O-2 = -0.72. The slightly lower ratios than those predicted
from the Redfield model have been attributed to the predominant production
of diatoms that have high concentrations of lipids. These results
suggest the following stoichiometry, 90 CO2 + 104 H2O + 14 HNO3 +
H3PO4 + 18 SiO2 --> (CH2O)(76)(CH2)(14)(NH3)(14)(H3PO4)(SiO2)(18)
+ 125 O-2 for the production of phytoplankton in the iron-enriched
patch. (C) 1998 Elsevier Science B.V. All rights reserved.
Tags
- co2;
- core;
- dioxide;
- equatorial
- fertilization;
- ice
- limitation
- marine;
- pacific-ocean;
- phytoplankton;
- scotia
- seas;
- southern-ocean;
