High Southern Native King

Core/Site name:

NCR 42, SCR 44, SAZ 47, SAF 51, PFZ 54

Country/Region:

Southern Ocean

Archive:

marine sediments (coretop)

Species:

G. bulloides, G. inflata, N. pachyderma (s)

Proxy measurement:

O18

Sampling resolution:

monthly

Climate sensitivity:

temperature, salinity

Startyear:

1996 AD

Endyear:

1998 AD

All uncertainties:

The Chatham Rise (NCR and SCR) samples were analysed at the Central Sciences Laboratory, University of Tasmania on an individual reaction-vial automated carbonate line coupled to a Micromass Optima mass spectrometer. Analytical precision was ±0.08 for d13C and ±0.09 for d18O (N = 51). The other samples (SAZ, SAF and PFZ) were analysed on a Micromass Optima at UC Davis. The average analytical precision for these measurements was ±0.05 for d13C, and ±0.06 for d18O (N = 28). The isotopic ratios are reported as per mil (‰) deviations from the Pee Dee belemnite (PDB) standard using Carrara marble as a laboratory standard.

Description:

The oxygen isotopic record obtained from Globigerina bulloides, Globorotalia inflata and Neogloboquadrina pachyderma (s.) was analysed for 5 sediment traps moored in the Southern Ocean and Southwest Pacific. The traps extend from Subtropical to the Polar Frontal environments, providing the first analysis of seasonal foraminiferal d18O records from these latitudes. Comparison between the foraminiferal records and various equations for predicted d18O of calcite reveals that the predicted d18O is best captured by the equations of Epstein et al. (1953) and Kim and O’Neil (1997). The Epstein equation shows a constant offset from the d18O of G. bulloides and N. pachyderma (s.) across the full range of latitudes. The seasonal range in d18O values for these two species implies a near-surface habitat across all sites, while G. inflata most likely dwells at ~50m depth. A significant finding in this study was that offsets from predicted d18O for G. bulloides do not correlate to changes in the carbonate ion concentration. This suggests that [CO32-] in and of itself may not capture the full range of carbonate chemistry conditions in the marine system. This sediment trap deployment also reveals distinct seasonal flux patterns for each species. Comparison between flux-weighted isotopic values calculated from the sediment traps and the isotopic composition of nearby surface sediments indicates that the sedimentary records retain this seasonal imprint. At the 51°S site, G. bulloides has a spring flux peak while N. pachyderma (s.) is dominated by summer production. The imprint of these differing seasonal production patterns on the flux-weighted d18O values results in more depleted d18O for N. pachyderma (s.) than for G. bulloides. Interpretations of N. pachyderma (s.) isotopic composition as a record of subsurface conditions may therefore need to be refined, with implications for interpretation of depleted glacial d13C for this species (Sigman and Boyle, 2000).

Data entered by name:

Bryan, Sean

Data entered by email:

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Main reference(s):

King, A.L. and Howard, W.R. 2005. d18O seasonality of planktonic foraminifera from Southern Ocean sediment traps: Latitudinal gradients and implications for paleoclimate reconstructions.Marine Micropaleontology. 56:1-24.

Link to reference 1:

http://www.sciencedirect.com/science/article/pii/S0377839805000174#sec3.1

Data storage link 1:

ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/king2005/king2005.txt

Comments:

Results for 5 sediment traps are reported. Locations are:NCR: 42°42’S;178°38’E SCR: 44°37’S; 178°37’E SAZ: 46°45.6’S; 142°4.2’E SAF: 51°0.01’S; 141°44.3’E PFZ: 53°44.8’S; 141°45.5’ETen specimens in the 250-355 µm size fraction were analysed per sample for G. bulloides and G. inflata, and 15-20 specimens in the 150-250 µm size fraction were analysed for N. pachyderma (s.).The King and Howard (2004) d13C data is available at: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/king2004/

Current dating method:

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Annual snow acc rate:

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Category: Ocean2k