Arctic Ocean Primary Productivity
K. E. Frey1, K. R. Arrigo2, R. R. Gradinger3
1Graduate School of Geography, Clark University, Worcester, MA, USA
2Department of Environmental Earth System Science, Stanford University, Stanford, CA, USA
3School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK, USA
November 8, 2011
Highlights
- Phytoplankton primary production in the Arctic Ocean increased ~20% from 1998-2009, mainly as a result of increasing open water extent and duration of the open water season. Increases in primary production were greatest in the eastern Arctic Ocean, particularly in the Kara (+70%) and Siberian (+135%) sectors.
- In addition to shifts in the total amount of production, new observations indicate an earlier timing of phytoplankton blooms in the Arctic Ocean (advancing up to 50 days over the 1997-2009 period) as well as community composition shifts towards a dominance of smaller phytoplankton species.
Sea ice melt and break-up during spring strongly drive primary production in the Arctic Ocean and its adjacent shelf seas by enhancing light availability as well as increasing stratification and stabilization of the water column. Recently observed dramatic declines in sea ice extent, thickness and annual persistence (see the essay on Sea Ice) should, therefore, have profound consequences for primary production throughout the region. Recent studies indeed document significant increases in primary production in several sectors of the Arctic Ocean, in addition to significant shifts in the timing and species composition of phytoplankton blooms.
Newly compiled satellite observations of primary production in the Arctic Ocean over a 12-year period (1998-2009) reveal a ~20% overall increase, resulting primarily from increases in open water extent (+27%) and duration of the open water season (+45 days) (Arrigo and van Dijken, 2011). However, no statistically significant secular trend in net primary production per unit area was found, stressing the overall importance of sea ice decline in driving these observed trends. Of the eight geographic sectors of the Arctic Ocean investigated (Fig. ME2, four exhibited statistically significant trends in primary production over the 12-year time period: Greenland (-13%), Kara (+70%), Siberian (+135%), and Chukchi (+48%). For the Arctic Ocean as a whole, annual phytoplankton primary production averaged 493 ± 41.7 Tg C yr-1 over the 1998-2009 period (based on direct satellite observations), as opposed to an estimate of 438 ± 21.5 Tg Cyr-1 over the 1979-1998 period (based on linear relationships with open water extent). However, these overall estimates are likely conservative, as they do not account for potential productivity that may occur within or beneath sea ice cover.
 |
| Fig. ME2. Trends in annual sea ice persistence (left) and total annual net primary production (right) across the Arctic Ocean and its adjacent shelf seas from 1998-2009. Sea ice persistence data (based on a 15% sea ice concentration threshold) are derived from Special Sensor Microwave/Imager passive microwave radiances (Cavalieri et al., 2008) and primary production data are from Arrigo and van Dijken (2011). |
In addition to phytoplankton primary production, sea ice algal production is also important to consider in the overall Arctic Ocean system. During periods of sea ice cover, total primary productivity is generally relatively small compared to estimates in open seas. As such, the central Arctic Ocean (with its historically multi-year ice cover) is one of the least productive marine regions on Earth, with annual primary production rates estimated at ~14 g C m-2 yr-1. During periods of ice cover, primary production by sea ice algae can be an important contributor to these overall production rates. Furthermore, release of ice algal material not only can act as a seed for phytoplankton blooms, but also may provide important food for pelagic and benthic biota (Leu et al., 2011). Annual estimates of the contribution of sea ice algal production to total production varies, with lowest contributions in the shelf seas (<10%) and highest contributions in the central Arctic Ocean (>50%) (Gosselin et al., 1997).
New observations of the timing of phytoplankton blooms in the Arctic Ocean show significant changes. Kahru et al. (2010) report significant trends towards earlier phytoplankton blooms for 11% of the area of the Arctic Ocean that is observable with satellite imagery over the 1997-2009 period. Areas experiencing earlier blooms in particular include those in the Hudson Bay, Foxe Basin, Baffin Sea, Greenland coasts, Kara Sea and near Novaya Zemlya, which are also areas roughly coincident with trends towards earlier sea ice break-up during early summer. In some of these regions, peak blooms in phytoplankton production have advanced from September to early July (a shift of up to ~50 days). Wassmann (2011) suggests that earlier sea ice retreats also cause earlier onset of the pelagic bloom, thus shortening the growth season of ice algae (which in turn is restricted to occur earlier because of critical limitations of available sunlight). The timing of phytoplankton and/or sea ice algal production is critical for the quantity and quality of primary production and associated grazers and therefore also the transfer of carbon and energy to higher trophic levels in both pelagic and benthic communities (Grebmeier et al., 2010, Tremblay et al., 2011; also see the essay on Marine Ecology: Biological Responses to Changing Sea Ice and Hydrographic Conditions in the Pacific Arctic Region).
The community composition of phytoplankton blooms in the Arctic has also shown measurable trends, with recent observations revealing shifts towards a dominance of smaller sized phytoplankton. With a freshening of the Arctic Ocean and associated reduction in the supply of nutrients, trends towards a dominance of smaller picophytoplankton over larger nanophytoplankton have been observed (Li et al., 2009). Even though the total amount of production may not change, a smaller community size structure of primary producers generally may not allow for large transfers of carbon up the food chain.
References
Arrigo, K. R., and G. L. van Dijken (2011), Secular trends in Arctic Ocean net primary production. Journal of Geophysical Research 116, C09011, doi:10.1029/2011JC007151.
Cavalieri, D., C. Parkinson, P. Gloersen, and H. J. Zwally (2008), Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.
Gosselin, M., M. Levasseur, P. A. Wheeler, R. A. Horner, and B. C. Booth (1997), New measurements of phytoplankton and ice algal production in the Arctic Ocean. Deep-Sea Research-II 44, 1623-1644.
Grebmeier, J. M., S. E. Moore, J. E. Overland, K. E. Frey, and R. R. Gradinger (2010), Biological response to recent Pacific Arctic sea ice retreats. Eos, Transactions, American Geophysical Union 91, 161-162.
Kahru, M., V. Brotas, M. Manzano-Sarabia, and B. G. Mitchell (2010), Are phytoplankton blooms occurring earlier in the Arctic? Global Change Biology, doi: 10.1111/j.1365-2486.2010.02312.x.
Leu, E., J. E. Søreide, D. O. Hessen, S. Falk-Petersen, and J. Berge (2011), Consequences of changing sea-ice cover for primary and secondary producers in the European Arctic shelf seas: Timing, quantity, and quality. Progress in Oceanography 90, 18-32.
Li, W. K. W., F. A. McLaughlin, C. Lovejoy, and E. C. Carmack (2009), Smallest algae thrive as the Arctic Ocean freshens. Science 326, 539.
Tremblay, J.-É., S. Bélanger, D. G. Barber, M. Asplin, J. Martin, G. Darnis, L. Fortier, Y. Gratton, H. Link, P. Archambault, A. Sallon, C. Michel, W. J. Williams, B. Philippe, and M. Gosselin (2011), Climate forcing multiplies biological productivity in the coastal Arctic Ocean, Geophys. Res. Lett., 38, L18604, doi:10.1029/2011GL048825.
Wassmann, P. (2011), Arctic marine ecosystems in an era of rapid climate change. Progress in Oceanography 90, 1-17.
