Agenda

Amos Winter, Department of Earth and Environmental Systems, Indiana State University (IN, USA)

Titolo: The deep photic zone, one of Earth’s least explored frontiers and one of the largest biomes on our planet

Abstract:
Satellite ocean maps of chlorophyll-a show and detect back-scattered light from phytoplankton from a layer only 70cm thick.  They show three distinct productive regions in the oceans 1) the western margins of continents, 2) equatorial regions, and 3) polar regions. However, there is a critical fourth region of phytoplankton biomass  concentration undetectable by satellite imagery often not considered or mis-represented in most biogeochemical modeling and observational studies. This deep photic layer occurs primarily in the tropical-subtropical ocean gyres. The extent of the deep photic biological community is not well constrained, but it should be extensive because ocean gyres alone account for about 60% of the total ocean area. Phytoplankton congregate in the lower photic layers of the ocean because they have at their disposal two critical parameters needed to sustain them: light from above and nutrients from below although it has now become apparent that many of the phytoplankton don’t need light and are heterotrophic (or mixotrophic). On a recent sampling collection trip to Bermuda we discovered c. 35 new coccolithophore species which represent about 15 percent of all coccolithophores so far observed in the ocean. Many of these species do not have chloroplasts. The deep photic species may represent a refugia community that can function as a seed community to replenish the surface communities when the conditions become untenable such as lowered pH and increased temperatures now taking place. We are working on determining any divergence in the genomic evolutionary tree between coccolithophores living in the deep photic zone. The existence of the deep photic coccolithophore communities likely also influences the biogeochemical cycling of carbon as is exemplified by the greater than average sizes of coccoliths being produced by the deep dwelling species, and the observation that the most abundant species that occupies this layer, Florisphaera profunda, is comprises the most important component of surface sediments in the world's ocean.

Bio Sketch:
Amos Winter is a professor at Indiana State University and currently visiting researcher at Ca' Foscari - DAIS. Previously he worked in the Department of Marine Sciences at the University of Puerto Rico at Mayaguez, where he was commonwealth climatologist for over 10 years. He was also a Program Officer in the Marine Geology Division at the National Science Foundation. He has written over 75 peer-reviewed articles covering numerous topics including climate data analysis and Quaternary climate reconstruction using proxies from corals, sclerosponges, and speleothems. His edited book “coccolithophores” is one of the world’s authoritative works for this important marine phytoplankton group.