Ocean Science

Warm and Salty Fingers

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Science  12 Dec 2003:
Vol. 302, Issue 5652, pp. 1865
DOI: 10.1126/science.302.5652.1865c

The stratified conditions found in fjords, bays, and many larger bodies of water inhibit vertical mixing of many ocean components, including O2. If O2 diffusion across a zone that separates layers of different density—called a pycnocline—is too slow to support the rate at which organic matter is oxidized, suboxic or anoxic conditions can develop in the deeper layers. In the Black Sea, a stable suboxic zone lies between the upper oxic waters, originating from Mediterranean inflow through the Bosporus Strait, and the deeper anoxic zone. However, the restricted mixing within this configuration means that the downward flux of O2 is insufficient to balance the upward flux of sulfide that is observed.

Konovalov et al. report the discovery of thin layers of oxygen-rich waters, extending as much as 200 km into the Black Sea, which inject massive amounts of O2 into the oxic and suboxic layers. These 5-m-thick “fingers” of oxygenated water are created by the mixing of colder and fresher Black Sea water with warmer and more saline Mediterranean water. On the basis of these observations, the authors suggest that lateral transport may be equally important in many other water bodies that exhibit permanent pycnoclines. — HJS

Limnol. Oceanogr. 48, 2369 (2003).

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