"dead carbon"
S2 (mgHC/gSed)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Total organic carbon (%)
HI´ =70 HI ´= 13 0
HI´ =9 5
"dead carbon"
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
In order to reconstruct changes in paleoproductivity, productivity, corrected for the amount of of C and C -plants, with a variability in relative 3 4 paleosea-surface temperatures, and terrigenous/ refractory ("dead") organic matter as obtained proportions constrained to proxies of ocean marine organic carbon input and their relationship from Rock-Eval pyrolysis (Fig. 2), reaches values circulation (Fig. 4).
-2 -1
to climate change, specific biomarkers (n-alkanes, of about 50 gC m y during peak interglacials The biomarker records display a distinct periodic fatty acids, alkenones, sterols), Rock-Eval pyrolysis (e.g., MIS 5e and lowermost MIS 11), which is variability which is related to Milankovich and sub- data, and stable carbon isotopes of the organic close to the modern productivity measured in Milankovich climate cycles (Fig. 5). Furthermore, a fractions (total C and biomarkers), as well as org the study area (Fig. 3). During glacial intervals, correlation with the Vostok temperature curve (Petit accumulation rates of organic carbon were the productivity was increased reaching values et al. 1999) and the SPECMAP climate record (Imbrie
-2 -1
determined in sediment samples from ODP Site 1089 of about 100-150 gC m y . These glacial/ et al. 1984) is obvious.
(Atlantic sector of the Southern Ocean; Gersonde, interglacial changes are explained by a The same type of work is in progress for ODP Site 1093, Hodell et al. 1999, Fig. 1). northward shift of the high-productivity zone located further to the south.
The investigated samples represent the time interval during glacials. During peak-interglacials, from Marine Oxygen Isotope Stages (MIS) 12 to 5e alkenone seasurface temperatures were about (i.e., about 450 to 100 ka). Based on the biomarker 6°C warmer than during glacials.
data, marine organic carbon was significantly Stable carbon isotopic analyses of the enriched during glacial stages. Estimated paleo- terrigenous n-alkanes identified a mixed origin
References:
Berger, W.H., Smetacek, V., Wefer, G. 1989. Productivity of the Ocean: Past and Present. Life Sciences Research Report 44, Wiley & Sons, New York, 471pp.
Chikaraishi, Y., Naraoka, H. 2003. Compound-specific dD-d13C- analyses of n-alkanes extracted from terrestrial and aquatic plants. Phytochemistry 63, 361-
371. 13
Collister, J.W., Rieley, G., Stern, B., Eglinton, G., Fry, B. 1994. Compound specific d C analyses of leaf lipids from plants with differing carbon dioxide metabolisms. Organic Geochemistry 21 (6/7), 619-627.
Gersonde, R., Hodell, D., Blum, P., Anderson, E.C., Austin, W., et al. 1999. Proc. ODP Int. Repts., 177: College Station, TX (Ocean Drilling Program).
Ghil, M., Allen, M.R., Dettinger, M.D., et al., 2002. Advanced spectral methods for climatic time series. Reviews of Geophysics 40, 41pp.
Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., Shackleton, N.J. 1984. The orbital theory of Pleistocene climate: Support from a revised chronology of the marine d18O record. In: Berger, A.L. et al. (Eds.), Milankovitch and Climate, Part I, Reidel, Norwell, MA, pp. 269-305.
Kuhn, G., Diekmann, B. 2002. Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089). Palaeogeography, Palaeoclimatology, Palaeoecology 182, 287-303.
Petit, J.R., Jouzel, J., Raynaud, D., et al. 1999. Climate and atmospheric history of the past 420.000 years from the Vostok ice core, Antarctica. Nature 399, 429- Rommerskirchen, F., Eglinton, G., Dupont, L., Güntner, U., Wenzel, C., Rullkötter, J. 2003. A north to south transect of Holocene southeast Atlantic continental 436.
margin sediments: Relationship between aerosol transport and compound-specific d13C land plant biomarker and pollen records. Geochemistry, Geophysics, Geosystems (G ) 4 (12), 29pp.3
Smith, W.H.F., Sandwell, D. T.1997. Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings. Science 277, 1956-1962.
Stein, R. 1986. Surface-water paleo-productivity as inferred from sediments deposited in oxic and anoxic deep-water environments of the Mesozoic Atlantic Ocean. In: Degens, E.T. et al. (eds), Biochemistry of Black Shales, Mitt. Geol. Paläont. Inst. Univ. Hamburg 60, 55-70.
Acknowledgements:
This study was funded by the Deutsche Forschungsgemeinschaft through grants STE 412/15 (PW) and STE 412/16-1 (JH).
Fig. 2: Correlation of total organic carbon (Kuhn & Diekmann, 2002) and S2-values from Rock-Eval pyrolysis (R = 0.844, n = 198). The intercept of the regression line (not shown) determines an amount of ca. 0.13% "dead"
(i.e. refractory) organic carbon. HI':
hydrogen index (S2x100/TOC), calculated after subtraction of "dead carbon".
Fig. 3: Total organic carbon (Kuhn & Diekmann, 2002), amount of brassicasterol (a diatom-derived organic compound), estimated paleoproductivity (according to the formula of Stein, 1986), and alkenone-derived sea-surface temperature (SST) for the time interval 100 to 450ka at ODP Site 1089. The records are correlated with the Vostok atmospheric temperature difference (DT, Petit et al., 1999) and the benthic d
18O SPECMAP stack (Imbrie et al., 1984). "Modern" values (top of the figure) derive from MUC-samples taken at the location of Site 1089.
Fig. 1: Study area showing the position of ODP Site 1089 and cited core locations in the southeastern South Atlantic. Arrows indicate independent surface and bottom ocean circu- lation pattern (adapted from Kuhn & Diekmann, 2002). Coloured regions of south Africa indicate simplified distribution of terrestrial plant-types.
Background image shows satellite derived gravity field (Smith & Sandwell, 1997).
Fig. 4: Amount of landplant-derived n-alkanes (S C ,C ,C ), carbon isotopic 27 29 31 composition of n-C alkane, and %-contribution of C -plants from binary mixing- 31 4 calculations assuming literature-derived C (-35.5‰) and C (-20.4‰) n-alkane 3 4 endmembers (Collister et al., 1994; Chikaraishi & Naraoka, 2003). The proportions of C -derived n-alkanes correlates with proxies for the variability of ocean circulation 4 (Kuhn & Diekmann, 2002), suggesting an origin from different continents for the terrigenous n-alkanes and thus obscuring the n-alkane record in terms of absolute amounts.
Fig. 5: Spectral analysis (MTM-SSA- toolkit, Ghil et al., 2002) of organic carbon records in Site 1089, compared to SPECMAP and Vostok DD. The analysed time window (100- 450ka) of the brassicasterol record shows relevant peaks for cycles connected to the precession (23ka), also present in the extended time range (0-600ka) of the paleopro- ductivity data. For these data, a prominent spectral peak occurs also with the eccentricity cycle (100ka), but is less obvious in the shorter brassicasterol record. In addition, a 29ka cycle is present in the brassica- sterol spectrum. The paleopro- ductivity data also show relevant spectral peaks at higher frequen- cies, partly correlating with the Vostok record.
PALEOPRODUCTIVITY, PALEOTEMPERATURE AND TERRIGENOUS INPUT IN THE MID-PLEISTOCENE SOUTHERN SOUTH ATLANTIC:
IMPLICATIONS FROM BIOMARKER RECORDS (ODP-SITE 1089)
Petra Weller, Jens Hefter, and Ruediger Stein
Alfred Wegener Institute for Polar and Marine Research Bremerhaven, Germany
(pweller@awi-bremerhaven.de) (jhefter@awi-bremerhaven.de) (rstein@awi-bremerhaven.de)
0 0.2 0.4 0.6 0.8 1 TOC (%)
100
150
200
250
300
350
400
450
0 5 10 15 20 25 30 Brassicasterol
(µg/g TOC)
0 50 100 150 200 Paleoproductivity
-2 -1
(gC m y )
-10 -5 0 5
Vostok DT (°C) (atmosphere)
modern surfacewater productivity (Berger et al., 1989)
25
10 15 20
Alkenone SST (°C)
modern SST age(ka)
-1 -0.5 0
0.5 1
SPECMAP d18O (‰)
100
150
200
250
300
350
400
MIS 450 12 10 8 6
mean subtr.
before stacking
"Modern" situation at Site 1089 (MUC-samples)
Brassicasterol
(µg/g TOC) Alkenone SST (°C)
10 15 20 25
depth (cm) depth (cm)
0 10 20 30
0 10 20 30 40
0 10 20 30 40
SOUTH ATLANTIC
SOUTHERN OCEAN 1089
1089
1084 1084 1722 1722
Agulhas Current
Agulhas Basin Angola
Basin
CapeBasin
Enderby Basin SW Indian Ridge
Benguela Current
INDIAN OCEAN
ACC Polar Front
ACC Subantarctic Front ACC Subtropical Front
Southern ACC-Boundary
Agulhas Ridge
Weddell Gyre
AABW Outflow
Mid Atlantic Ridge
Walvis Ridge
-20° -10° 0° 10° 20° 30° 40°
-20°
-30°
-40°
-50°
-60°
C < 5%4 20% < C < 40%4 C > 60%4 C +C < CAM3 4 Simplified modern phytogeographical units of southwest Africa
(Rommerskirchen et al., 2003)
this study
Rommerskirchen et al., 2003 ODP
GeoB
OCEAN CIRCULATION surface
currents bottom-contour currents
(1093) (1093)
40 45 50 55 60 calc. % of C -Alkane31
from C -plants4
-30 -29 -28 -27 -26 d13C (‰)
C 31 n-alkane
0.5 0.8 1.0 1.2 1.5 1.8 Kao/Chl-Ratio
2 3 4 5 6 7
Qz/Fsp-Ratio
0 100 200
0 10 20 30 depth (cm) 40
S terr. n-alkanes (µg/g TOC) age(ka)
0 100 200
100
150
200
250
300
350
400
450
northwards
displacement of NADW southwards
strong
weak strong
weak
leakage of Agulhas Current to South Atlantic (Kuhn & Diekmann, 2002)
South America South Africa
proposed origin of plant
n-alkanes
Site 1089
(MUC-samples) ODP 1084 2.5 ka: 65% C
4GeoB 1722 6.8ka: 50% C
4(Rommerskirchen et al., 2003)
"Modern" situation
-1 -0.5 0
0.5 1
SPECMAP d18O (‰)
100
150
200
250
300
350
400
MIS 450 12 10 8 6
mean subtr.
before stacking
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0
100 200
300 d18O SPECMAP
(0-600ka)
0 5 10
15 Paleoproductivity
(0-600ka)
frequency (1/ka) spectral density (harmonic/median)
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
F-test level
99%95%
0 5 10 15 20
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Brassicasterol
(100-450ka)
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0
2 4 6
8 Vostok DD
(0-420ka)
100 ka 41 ka 29 ka 23 ka 19 ka
3.8-3.3ka 2.8ka 2.5-2.3ka
