FN Archimer Export Format
PT J
TI Silicic acid dynamics in the glacial sub-Antarctic: Implications for the silicic acid leakage hypothesis
BT 
AF BEUCHER, Charlotte P.
   BRZEZINSKI, Mark A.
   CROSTA, Xavier
AS 1:1;2:2;3:3;
FF 1:;2:;3:;
C1 Univ Calif Santa Barbara, Marine Sci Inst, Santa Barbara, CA 93106 USA.
   Univ Calif Santa Barbara, Dept Ecol Evolut & Marine Biol, Santa Barbara, CA 93106 USA.
   Univ Bordeaux 1, EPOC, CNRS, UMR 5805, F-33405 Talence, France.
C2 UNIV CALIF SANTA BARBARA, USA
   UNIV CALIF SANTA BARBARA, USA
   UNIV BORDEAUX, FRANCE
IF 4.335
TC 66
UR https://archimer.ifremer.fr/doc/00233/34462/32882.pdf
LA English
DT Article
CR APSARA 1 - MD 31
   APSARA 2/ANTIPROD 3-MD 38
   APSARA 3 - MD 54
   APSARA 4 - MD 56
   IMAGES 3-IPHIS-MD106
BO Marion Dufresne
DE ;silicon isotope;silicic acid leakage;Indian sub-Antarctic
AB The silicic acid leakage hypothesis (SALH) purports that changes in silicon and nitrogen depletion ratios in the glacial Antarctic created a large pool of unused silicic acid that was transported to lower latitudes in subantarctic mode water (SAMW) where it enhanced diatom productivity lowering atmospheric pCO(2). However, increased opal accumulation beneath the sub-Antarctic during glacial times implies significant consumption of silicic acid in subantarctic surface waters that may have significantly diminished or eliminated Si leakage. To test how nutrient dynamics in the sub-Antarctic affected the Si( OH) 4 content of SAMW during the last glacial period, we produced delta(30) Si opal records for cores from the subantarctic and subtropical zones of the Indian Ocean spanning the last 50,000 years. Comparison with diatom-bound delta N-15 records shows that subantarctic surface waters were enriched in Si relative to N during the last glaciation consistent with the SALH. The record from the subtropics does not show this enrichment in Si during the last glacial period suggesting that subantarctic surface waters were mainly incorporated into SAMW rather than being transported across the Subtropical Front. Isotope mass balance calculations were used to test for Si leakage from the sub-Antarctic. The results show that silicic acid concentration in SAMW would more than double during the last glaciation if upwelling and northward Ekman drift in the Antarctic were similar to the present-day circulation. Calculations that assume increased stratification in the glacial Antarctic eliminate Si leakage, but they do not produce the known increase in opal burial in the glacial sub-Antarctic. Reconciling the isotope data and opal burial records with a highly stratified Antarctic requires the addition of a large local source of silicic acid in the glacial sub-Antarctic that is inconsistent with present-day circulation and nutrient distributions. Including such a source in our calculations results in significant opal burial in the sub-Antarctic, but it does not enhance Si leakage over that occurring in the Holocene. Resolving past changes in the circulation of the Southern Ocean is clearly vital to future tests of the SALH.
PY 2007
PD AUG
SO Global Biogeochemical Cycles
SN 0886-6236
PU Amer Geophysical Union
VL 21
IS 3/GB3015
UT 000249335000001
BP 1
EP 13
DI 10.1029/2006GB002746
ID 34462
ER

EF