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Ocean Biogeophysical Conditions

M. Yamamoto-Kawai1, W. Williams2, S. Nishino3, F. McLaughlin2

1Tokyo University of Marine Science and Technology, Tokyo, Japan
2Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, British Columbia, Canada
3Japan Agency for Marine-Earth Science and Technology, Tokyo, Japan

November 8, 2011

Highlights

  • In 2010 and 2011, the nutricline and associated chlorophyll maximum were slightly less deep than in 2009, but still significantly deeper than in 2003-2007. This is consistent with the slight relaxation of the Beaufort Gyre since 2009 (see the essay on Ocean).
  • Undersaturation of the surface waters of the Canada Basin with respect to aragonite, a form of calcium carbonate found in plankton and invertebrates, was first observed in 2008. The areal extent of undersaturated surface water in 2011 was similar to that in 2010 (see the essay on Ocean Acidification).

As described in the Ocean essay, the quantity of fresh water stored in the Beaufort Gyre increased substantially in 2004-2005, 2006-2007 and 2007-2008, and has remained at high levels since 2008. These increases in freshwater content are due to inputs of sea-ice melt water (Yamamoto-Kawai et al. 2009) and strong Ekman pumping conditions (updates to Proshutinsky et al. 2009 and Yang 2009), and have increased the depth of the upper halocline in the interior of the Canada Basin (Fig. ME1a), freshened the surface waters (Fig. ME1b) and increased surface layer stratification (Fig ME1c). Consequently, there is a deeper nutricline and a deeper subsurface chlorophyll maximum, a feature that is closely associated with the top of the nutricline in summer and fall (Fig. ME1d; McLaughlin and Carmack 2010). In 2010 and 2011, the chlorophyll maximum and nutricline were slightly shallower than in 2009, but still significantly deeper than in 2003-2007. This is consistent with the slight relaxation of the Beaufort Gyre since 2009.

Fig. 1 -- Average properties in the Beaufort Gyre region
Fig. ME1. Average properties in the Beaufort Gyre region of the Canada Basin as observed by the Joint Ocean Ice Studies Expeditions: (a) average depth of the 33.1 isohaline; (b) mean salinity at 2-40 m depth; (c) average salinity stratification between 5-100m; (d) depth of the sub-surface chlorophyll maximum at the top of the nutricline.

These changes in the Beaufort Gyre are expected to stress biological production. Increased stratification is thought to lead to a reduction of overall nitrate fluxes into the mixed layer, a condition that limits new biological production and favors smaller organisms at the base of the food web (Li et al. 2009), while a deeper upper halocline further removes the nutricline and chlorophyll maximum from sunlight increasing the importance of light limitation.

In 2010, a large warm-core eddy was observed in the southwestern Canada Basin. This eddy carried ammonium from the shelf to the basin to sustain a higher biomass of picophytoplankton within the eddy (Nishino et al., 2011a). Such episodic transport of nutrients from the shelf to the Canada Basin by eddies is likely now more important to biological production as the nutricline is now deeper and those nutrients less available.

Biological productivity may be enhanced outside of the Beaufort Gyre in the Arctic Ocean. In the basins (e.g., Makarov Basin), this could be due to the nutrient supply from the shelves and greater light penetration for photosynthesis caused by the sea ice loss (see the essay on Sea Ice) (Nishino et al., 2011b). Over the Canadian and Alaskan Beaufort shelves, the same wind-forcing that drives Ekman convergence in the Beaufort Gyre is responsible for shelfbreak upwelling, which can act to bring nutrient-rich Pacific-origin water from depth into the euphotic zone (Carmack and Chapman 2003; Williams and Carmack 2008; Tremblay et al., 2011). Waters along these continental shelves are thus expected to become more productive because of increased exposure to upwelling favorable wind enhanced by reduced ice extent and a more mobile ice pack that is more responsive to wind forcing (Yang 2009; Carmack and Chapman 2003).

Undersaturation of the surface waters of the Canada Basin with respect to aragonite, a form of calcium carbonate found in plankton and invertebrates, was first observed in 2008 (Yamamoto-Kawai et al., 2009). This rapid and large decrease in aragonite saturation state was caused by a combination of increased atmospheric CO2 and melting of sea ice. The increased amount of open water (see the essay on Sea Ice) enhanced the uptake of CO2 from the atmosphere and the freshening of the upper ocean (see the essay on Ocean) decreased alkalinity, inorganic carbon and calcium ion concentrations (Yamamoto-Kawai et al., 2011). Although CO2 concentration in surface waters in 2010 and 2011 was not as high as in 2008 (Cai et al., 2009), these waters have continued to be undersaturated with respect to aragonite. The areal extent of undersaturated surface water in 2011 was similar to that in 2010. For more information on ocean acidification, see the essay on The Extent and Controls on Ocean Acidification in the Western Arctic Ocean and Adjacent Continental Shelf Seas.

References

Cai, W.-J., et al., 2010, Decrease in the CO2 uptake capacity in an ice-free Arctic Ocean Basin, Science, 329, 556-559, doi:10.1126/science.1189338.

Carmack, E. C. and D. C. Chapman, 2003, Wind-driven shelf/basin exchange on an Arctic shelf: The joint roles of ice cover extent and shelf-break bathymetry, Geophys. Res. Lett., 30, 1778 doi:10.10.1029/2003GL017526.

Li W.K., F.A. McLaughlin, C. Lovejoy, E.C. Carmack, 2009: Smallest Algae Thrive As the Arctic Ocean Freshens, Science, Vol. 326. no. 5952, p. 539 doi:10.1126/science.1179798.

McLaughlin, F. A. and E. C. Carmack, 2010: Deepening of the nutricline and chlorophyll maximum in the Canada Basin interior, 2003-2009, Geophys. Res. Lett., 37, L24602, doi:10.1029/2010GL045459.

Nishino, S., M. Itoh, Y. Kawaguchi, T. Kikuchi, and M. Aoyama, 2011a; Impact of an unusually largewarm-core eddy on distributions of nutrients and phytoplankton in the southwestern Canada Basin during late summer/early fall 2010, Geophys. Res. Lett., 38, L16602, doi:10.1029/2011GL047885.

Nishino, S., T. Kikuchi, M. Yamamoto-Kawai, Y. Kawaguchi, T. Hirawake, and M. Itoh, 2011b; Enhancement/reduction of biological pump depends on ocean circulation in the sea-ice reduction regions of the Arctic Ocean, J. Oceanogr., 67, 305-314, doi:10.1007/s10872-011-0030-7.

Proshutinsky, A., R. Krishfield, M.-L. Timmermans, J. Toole, E. Carmack, F. McLaughlin, W. J. Williams, S. Zimmermann, M. Itoh, and K. Shimada, 2009: Beaufort Gyre freshwater reservoir: State and variability from observations J. Geophys. Res., doi:10.1029/2008JC005104.

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.

Williams, W. J. and E. C. Carmack, 2008: Combined effect of wind-forcing and isobath divergence on upwelling at Cape Bathurst, Beaufort Sea, Journal of Marine Research, 66, 645-663.

Yamamoto-Kawai, M., F. A. McLaughlin, E. C. Carmack, S. Nishino, K. Shimada, 2009: Aragonite Undersaturation in the Arctic Ocean: Effects of Ocean Acidification and Sea Ice Melt, Science, Vol. 326. no. 5956, pp. 1098-1100, doi: 10.1126/science.1174190.

Yamamoto-Kawai, M., M., F. A. McLaughlin, and E. C. Carmack (2011), Effects of ocean acidification, warming and melting of sea ice on aragonite saturation of the Canada Basin surface water, Geophys. Res. Lett., 38, L03601, doi:10.1029/2010GL045501.

Yang, J., 2009: Seasonal and interannual variability of downwelling in the Beaufort Sea, J. Geophys. Res. , 114 , C00A14, doi:10.1029/2008JC005084.