Potential biogeochemical effects from vigorous internal tides generated in Luzon Strait: A case study at the southernmost coast of Taiwan

Abstract

Vigorous internal tides excited in the Luzon Strait are the putative cause of regular temperature drops of 2-10°C within only 12-24 h at the southernmost coast of Taiwan. Significant amounts of nutrient pumping, i.e., 2.4-22.9 mmol N m-2 h1 nitrate (NO3-) and 0.4-1.75 mmol P m-2 h-1 phosphate (PO43-), occur during the upward phase in an internal tide. The upwelling, which is potentially induced by internal tides, not only helps cap the summertime mean temperature at ∼27.6°C but also supplies nutrients to the euphotic layer, which may be beneficial to the growth of coral reefs. A baroclinic tide model with 1°/12 (∼9.2 km) resolution, which is sufficient to resolve topography around southern Taiwan, was used to evaluate the internal tide generation in the Luzon Strait and the physical and biogeochemical influences of these tides in this coastal region. The timing and amplitude, as well as fortnightly and seasonal variations of the modeled temperatures, agreed with the observations, suggesting that observed temperature decreases and nutrient enrichment are primarily caused by internal tide-induced upwelling. This investigation further indicated that the internal tides propagating to the coast are remotely generated on the eastern flank of Heng-Chun Ridge, rather than locally, near the southernmost coast of Taiwan. The model also evaluated that the seasonal variation of the pycnocline in the receiving waters, which is stronger and shallower during summer than winter, results in relatively larger temperature decreases in the summer. Copyright 2009 by the American Geophysical Union.