25th International Meeting on Organic Geochemistry IMOG 2011

P-213
Biomarker proxies indicate silicic acid transport from the
Southern Ocean to southeastern Australia during interglacials
Raquel Lopes dos Santos 1 , Daniel Wilkins 2 , Patrick De Deckker 2 , Stefan Schouten 1
1 Royal Netherlands Institute for Sea Research (NIOZ), Texel, Netherlands, 2 The Australian National
University (ANU), Canberra, Australia (corresponding author:raquel.santos@nioz.nl)
The Southern Ocean (SO) has been
identified as having a major role in regulating
productivity at lower latitudes due to the formation of
different water masses that transport nutrients to
other oceans. For instance, silicic acid is thought to
be an important nutrient leaked from the SO during
glacials via intermediate waters and stimulate
phytoplankton production at mid to lower latitudes.
Additionally, planktonic foraminiferal carbon isotope
minima during deglaciations have been observed in
numerous cores from the southern hemisphere (SH)
mid-lower latitudes and has been suggested as an
isotopical signal of upwelled deep SO waters.
Here we compared planktonic � 13 C of
Globigerina bulloides with organic proxy records for
Proboscia diatom (1,14-diol index) and haptophyte
algae abundances (alkenones) from a core in the
Murray Canyons region of South East Australia (SEA)
to estimate the influence of deep SO waters in the
productivity of SEA. The Diol index is based on the
ration of 1,14 diols, lipids produced by Proboscia
diatoms and 1,15 diols, lipids related to unidentified
algae, possibly Eustigmatophytes. For haptophyte
abundances, we measured alkenones distribution,
lipid specific for this group of algae.
Our result shows that although SO waters
were upwelled during deglaciations, as revealed by
foraminifera isotopic minima, this did not result in
increased productivity. Instead, Proboscia diatoms
proliferated after the � 13 C minima during interglacials
and MIS 3, likely because silicic acid was leaked to
this area only after a SO decrease in diatom
production. Furthermore, haptophyte algae only
proliferated when Proboscia diatom productivity
decreased suggesting that silicic acid concentration
was insufficient for the needs of Proboscia.
Thus, our study suggests a wider
distribution of silicic acid leakage during glacialinterglacial
cycles likely controlled by the intensity of
water masses transporting this nutrient.
Fig. 1 Comparison of geochemical records of core
MD03-2607 from southeastern Australia with the opal
flux record of a core in the SO. A) U K‘ 37 sea surface
temperature, B) planktonic � 13 C of Globigerina
bulloides, C) Diol index, D) alkenones concentration
and E) Opal flux record from SO. Blue shaded area
indicate periods of depleted planktonic � 13 C
suggesting input of deep SO waters in the Murray
Canyons region.
� 13 C G.bull.
MD03-2607
Alkenones 37:2+37:3
[ng/g sed.]
OPAL flux TN057-13
[g cm -2 kyr -1 ]
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
80
60
40
20
0
7
6
5
4
3
2
1
0
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
Age [kyrs]
A
B
C
D
E
22
20
18
16
14
12
10
8
0.6
0.4
0.2
0.0
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
Diol index
MD03-2607
OPAL flux TN057-14
[g cm -2 kyr -1 ]
352
U K'
37 SST
[ 0 C]