Variability and timing of glacial-interglacial productivity in the polar North and South Pacific - Implications for global climate development (PROPAC)

PROPAC was originally designed as a three years project to

• reconstruct the timing and magnitude of glacial/interglacial variability of biological productivity in the polar South and North Pacific and reveal East-West gradients in relation to dust sources (iron deposition), sea ice extent and ocean ventilation over the past two terminations; and

• synchronize and compare the records with Greenland and Antarctic ice core CO2 and dust records to estimate the response/role of polar Pacific “high nutrient-low chlorophyll” (HNLC) areas to/in glacial climate development.

It was proposed to base the reconstructions on a paleobiological (diatoms/ dinoflagellates) approach, supported by geochemical (δ15Ndiat) data. Appropriate core material was recovered during RV Sonne cruise 202 (INOPEX, 7.7. - 28.8.2009) in the polar North Pacific and Bering Sea, and RV Polarstern cruise ANT-XXVI/2 (BIPOMAC, 2.12.2009 - 3.2.2010, for cruise report see http://epic.awi.de/epic/) in the polar South Pacific. Obtained results were to be compared with a study from the Atlantic sector of the Southern Ocean. The project could not be continued after the first year because of the imposition of new application regulations as advised by written communication by the DFG.



PROPAC study areas (white rectangles) in polar “high nutrient/low chlorophyll” (HNLC) areas indicated by low pigment concentration (chlorophyll-a) in surface waters (A) and high concentrations of the nutrient nitrate at 10 m water depth.



PROPAC study areas (white rectangles) and simulated dust deposition in the World Ocean, modern (A) Last Glacial Maximum (B) (after Mahowald et al., 2006). Dashed lines indicate the water column integrated input of dissolved iron from mineral dust [mmol Fe m-2 year-1] (after Moore and Braucher, 2008). Low LGM dust deposition into the polar South Pacific is questioned by sediment records obtained during expedition ANT-XXVI/2 (Gersonde et al. 2011).



Combined record of northern and southern hemisphere dust/iron records from chinese loess (A), central Greenland ice core NGRIP (B), and Antarctic ice core EDC iron (C) and dust (D) (a: Sun and Huang, 2006; b: Ruth et al., 2007; c: Wolff et al., 2006; d: Ruth et al, 2008).

Results

First step within PROPAC was the completion of the paleobiological study of two sediment cores recovered in the Atlantic Southern Ocean on a transect between the Antarctic and the Subantarctic Zone. As shown by Abelmann et al. (2006), the relative abundance of two diatom species/species groups (Chaetoceros spp., Fragilariopsis kerguelensis) with different life strategies document distinct glacial and interglacial productivity regimes characterized by high carbon/low biogenic opal and low carbon/high biogenic opal export, respectively. Increased glacial accumulation rates of protoperidinioid dinoflagellate cysts, a group of dinoflagellates specialized to feed on Chaetoceros, support the establishment of a high carbon/low biogenic opal productivity regime in the glacial Southern Ocean, at conditions with increased availability of the micro-nutrient iron. However, the preservation of the protoperidinioid dinocysts in the sedimentary record also depends on the oxygenation at the sediment/water interface (e.g. Zonneveld et al. 2007). The obtained data are interpreted to indicate the presence of low-oxygen bottom waters in the glacial Southern Ocean, which may be caused by increased organic carbon deposition and reduced bottom water ventilation.

To extent this study to the Pacific Southern Ocean and the polar North Pacific, one core from each region was analysed. Unfortunately a combined study of diatom and dinoflagellate cyst assemblages across terminations I and II was not possible because of the absence of dinoflagellate cysts in the sedimentary record, except for intervals assigned to Marine Isotope Stage 5.5, a peak warm period. The reasons for the absence of dinoflagellate cysts in the studied records remain unresolved.

Scientists

Rainer Gersonde
Oliver Esper
Alfred-Wegener-Institute Bremerhaven

Karin Zonnefeld
MARUM/Fachbereich 5-Geowissenschaften, Universität Bremen

Research areas

Western North Pacific (51°N, 167°E)
Southern Ocean, South Pacific Sector (61°S, 116°W)
Southern Ocean, Atlantic Sector (53°S, 5°E)

Publications

Abelmann A, Gersonde R, Cortese G, Kuhn G, Smetacek V, 2006. Extensive phytoplankton blooms in the Atlantic Sector of the glacial Southern Ocean, Paleoceanography 21, doi:10.1029/2005PA001199.

Gersonde R, et al., 2011. The Expedition of the Research Vessel "Polarstern" to the polar South Pacific in 2009/2010 (ANT-XXVI/2 - BIPOMAC). Reports on Polar and Marine research, 632. hdl:10013/epic.37910.

Mahowald NM, Muhs DR, et al., 2006. Change in atmospheric mineral aerosols in response to climate: Last glacial period, preindustrial, modern, and double carbon dioxide climates. J. Geophys. Res. 111, D10202, doi:10.1029/2005JD006653.

Moore JK, Braucher O, 2008. Sedimentary and mineral dust sources of dissolved iron to the world ocean. Biogeosci. 5, 631-656.

Ruth U, Bigler M, et al., 2007. Ice core evidence for a very tight link between North Atlantic and east Asian glacial climate. Geophys Res. Letters 34, L03706, doi:10.1029/2006GL027876.

Ruth U, Barbante C, et al., 2008. Proxies and measurement techniques for mineral dust in Antarctic ice cores. Environ. Sci. Technol. 42, 5675-5681.

Sun J, Huang X, 2006. Half-precessional cycles recorded in Chinese loess: response to low-latitude insolation forcing during the Last Interglaciation. Quat. Sci. Rev. 25, 1065-1072.

Wolff EW, Fischer H, et al., 2006. Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles. Nature 440, 491-496.

Zonneveld KAF, Bockelmann F, Holzwarth U, 2007. Selective aerobic degradation of organic-walled dinoflagellates as a tool to quantify past net primary production and bottom water oxygen concentrations. Mar. Geol. 237: 109-126.

Homepage

http://www.awi.de/
http://www.geo.uni-bremen.de/

Research funding organisation

German Research Foundation

Project numbers: GE516/12-1, ZO144/4-1
Funding period: 2007 - 2010