Effect of seafloor depth on phytoplankton blooms in high-nitrate, low-chlorophyll (HNLC) regions

• Published in: Journal of Geophysical Research: Biogeosciences
• Main Authors: Tyrrell, T., Merico, A., Waniek, J. J., Wong, C. S., Metzl, N., Whitney, F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Geophysical Union 2005
• Subjects: phytoplankton; ocean color; bathymetry; HNLC; North Pacific; iron; Bering Sea; Pacific; Western Basin; Subarctic
• Online Access: https://archimer.ifremer.fr/doc/00232/34337/32758.pdf; https://doi.org/10.1029/2005JG000041; https://archimer.ifremer.fr/doc/00232/34337/

We calculated correlations between seafloor depth and phytoplankton blooms in all three main high-nitrate, low-chlorophyll (HNLC) regions, but with a particular focus on the subarctic North Pacific area. It has long been known that the central parts of the east and west subarctic North Pacific are HNLC regions. The deep western basin of the Bering Sea is also HNLC, whereas the wide continental shelf of the eastern Bering Sea is not. We carried out a statistical comparison of spatial maps of (1) seafloor depth and (2) chlorophyll a concentration from satellite data. This comparison reveals that shallow waters have, on average, higher peak chlorophyll a concentrations (more intense phytoplankton blooms) than deep waters (p << 0.01). Possible artifacts of the satellite data are considered but it is concluded that the signal is genuine, in part because the same patterns are found in in situ data. There are several possible explanations for the observed correlation; the most probable, we suggest, is that iron diffusing out of the seafloor causes alleviation of iron limitation in shallow waters.