Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 11, 15-25, 2015
http://www.clim-past.net/11/15/2015/
doi:10.5194/cp-11-15-2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
06 Jan 2015
Photic zone changes in the north-west Pacific Ocean from MIS 4–5e
G. E. A. Swann1 and A. M. Snelling2 1School of Geography, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
2NERC Isotope Geosciences Facilities, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
Abstract. In comparison to other sectors of the marine system, the palaeoceanography of the subarctic North Pacific Ocean is poorly constrained. New diatom isotope records of δ13C, δ18O, δ30Si (δ13Cdiatom, δ18Odiatom, and δ30Sidiatom) are presented alongside existing geochemical and isotope records to document changes in photic zone conditions, including nutrient supply and the efficiency of the soft-tissue biological pump, between Marine Isotope Stage (MIS) 4 and MIS 5e. Peaks in opal productivity in MIS 5b/c and MIS 5e are both associated with the breakdown of the regional halocline stratification and increased nutrient supply to the photic zone. Whereas the MIS 5e peak is associated with low rates of nutrient utilisation, the MIS 5b/c peak is associated with significantly higher rates of nutrient utilisation. Both peaks, together with other smaller increases in productivity in MIS 4 and 5a, culminate with a significant increase in freshwater input which strengthens/re-establishes the halocline and limits further upwelling of sub-surface waters to the photic zone. Whilst δ30Sidiatom and previously published records of diatom δ15N (δ15Ndiatom) (Brunelle et al., 2007, 2010) show similar trends until the latter half of MIS 5a, the records become anti-correlated after this juncture and into MIS 4, suggesting a possible change in photic zone state such as may occur with a shift to iron or silicon limitation.

Citation: Swann, G. E. A. and Snelling, A. M.: Photic zone changes in the north-west Pacific Ocean from MIS 4–5e, Clim. Past, 11, 15-25, doi:10.5194/cp-11-15-2015, 2015.
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Short summary
New diatom isotope records are presented alongside existing geochemical and isotope records to document changes in the photic zone, including nutrient supply and the efficiency of the soft-tissue biological pump, between MIS 4 and MIS 5e in the subarctic north-west Pacific Ocean. The results provide evidence for temporal changes in the strength and efficiency of the regional soft-tissue biological pump, altering the ratio of regenerated to preformed nutrients in the water.
New diatom isotope records are presented alongside existing geochemical and isotope records to...
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