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Transient stratification as the cause of the North Pacific productivity spike during deglaciation

Nature Geoscience volume 6, pages 622–626 (2013)Cite this article

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Abstract

During the Bølling–Allerød warm period of the last deglaciation, about 14 kyr ago, there was a strong and pervasive spike in primary productivity in the North Pacific Ocean1. It has been suggested that this productivity event was caused by an influx of the micronutrient iron from surrounding continental shelves as they were flooded by sea-level rise2. Here we test this hypothesis by comparing numerous proxies of productivity with iron flux and provenance measured from a core from the subarctic Pacific Ocean. We find no evidence for an abrupt deglacial pulse of iron from any source at the time of peak productivity. Instead, we argue that the deglacial productivity peak was caused by two stepwise events. First, deep convection during early deglaciation increased nutrient supply to the surface but also increased the depth of the mixed layer, which pushed surface production deeper in the water column and induced light limitation. A subsequent input of meltwater from northern American ice sheets then stratified the water column, which relieved light limitation while leaving the surface waters enriched in nutrients. We conclude that iron plays, at most, a secondary role in controlling productivity during the glacial and deglacial periods in the subarctic Pacific Ocean.

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Figure 1: Detrital provenance reconstructions based on Sr and Nd isotopic composition.
Figure 2: Multiproxy downcore records.
Figure 3: Map of study area showing endmember ɛNd, modelled wind and sea level at key climate periods.
Figure 4: Schematic to illustrate vertical mixing, nutrient and light levels during the Holocene, mid-deglaciation (14 kyr ago), early deglaciation (18 kyr ago) and during the LGM.

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Acknowledgements

This work was supported by the Lawrence J. Pratt and Melinda M. Hall Endowed Award for Interdisciplinary Research to L.F.R., P.J.L. and J.B.; the Marie-Curie Reintegration programme, European Research Council no. 278705 to L.F.R.; National Science Foundation (NSF) to P.J.L.; the Centre for Climate Dynamics at the Bjerknes Centre to C.L.; the Comer Science and Education Fund and the US NSF to J.F.M.; and NSF OCE-1031224 to L.D.K. Thanks to J. Goudreau for U-series help, E. Crapster-Pregont, J. Swartz, D. Ohnemus and M. Auro for sediment leaches, M. Carman for assistance with foraminiferal abundance counts, C. M. Bitz for providing ocean boundary conditions for the 14 kyr simulation and C. Lamborg, J. Rae and A. Mahadevan for stimulating discussions.This is publication no. A423 from the Bjerknes Centre for Climate Research.

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Authors and Affiliations

  1. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540, USA

    Phoebe J. Lam & Laura F. Robinson

  2. University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK

    Laura F. Robinson

  3. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540, USA

    Jerzy Blusztajn & Lloyd D. Keigwin

  4. Geophysical Institute, University of Bergen, 5007 Bergen, Norway

    Camille Li

  5. Bjerknes Centre for Climate Research, 5007 Bergen, Norway

    Camille Li

  6. Department of Geosciences, Williams College, Williamstown, Massachusetts 01267, USA

    Mea S. Cook

  7. Lamont Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA

    Jerry F. McManus

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Contributions

P.J.L., L.F.R. and J.B. conceived the project. L.F.R. conducted U-series measurements; J.B. conducted Nd and Sr isotope measurements; C.L. provided G.C.M. output; J.F.M. measured sediment composition; M.S.C. provided the age model and foraminiferal abundances; L.D.K. provided volcanic ash shard counts; P.J.L. measured soluble Fe and wrote the paper; all helped with interpretations and commented on the manuscript.

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Correspondence to Phoebe J. Lam.

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The authors declare no competing financial interests.

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Lam, P., Robinson, L., Blusztajn, J. et al. Transient stratification as the cause of the North Pacific productivity spike during deglaciation. Nature Geosci 6, 622–626 (2013). https://doi.org/10.1038/ngeo1873

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