Vertical advection from oxic or anoxic water from the main pycnocline as a cause of rapid extinction or rapid radiations

Abstract

The vast majority of oceanic biomass lives in the surface wind-mixed layer (0–100 m) of the ocean, trophically dependent on light or primary production based on photosynthesis. Waters from the main pycnocline (100–1000 m) or deeper naturally contain decay products from sinking organic matter as a function of the oxidation state of the waters. Such products, in proper concentrations, can inhibit photosynthetic growth or are toxic or debilitating to respirors. Usually, physical oceanographic processes of vertical circulation are slow or volumetrically small enough to permit “conditioning ”or mixing of toxicants of the deep waters with surface waters so that the deleterious effects of deep water are neutralized or localized. However, rapid global to regional scale vertical advection of deep waters into the surface mixed layer could create an ecologic crisis for various marine groups through a combination of: (1) direct toxicity; (2) reduction or modification of nutrient and food supplies through inhibition of photosynthesis; (3) chronic debilitation caused by contact with such toxic waters; or (4) increased predation by more adaptive or less effected taxa. Such events are not necessarily universally deleterious as they could offer new opportunities for taxa ecologically restricted under prior conditions. During cool climates with oxic deep waters, a crisis may be caused by upwelling of metals concentrated with depth and resulting in reduced primary productivity, as well as metal toxic and/or chronic reactions in higher groups. During warm climates with anoxic to dysaerobic waters in the pycnocline, a crisis may result from contact with anoxic waters with a maximum effect on respirors and a minimal to enhanced effect on phytoplankton. Upwelling may come from three redox zones: I- oxic; II- nitric; and III- sulfatic. Each zone would be the source of waters of differing chemistries that could be advected into the photic zone. The effect on specific taxa will be selective as a function of the depth and volume of source water, as different organisms have different tolerance limits or preadaptive capabilities. In the geologic record, significant upwelling events would be recorded initially as a general reduction in diversity, followed by mass extinctions in some groups and the possibility of rapid radiation in opportunistic groups. The ecologic requirements of both the extinct taxa and the newly enhanced taxa might be used to identify the type of any given major upwelling event.