Coastal phytoplankton in a global changing world, oceanic and terrestrial factors

Abstract

Phytoplankton production is largely determined by the availability of nutrients. In the open ocean, nutrient availability is largely determined by the mechanical energy needed to bring nutrient-rich deep water mixed with upper ocean surface water, marking a clear seasonal cycle, at least in temperate and subtropical seas. As the surface waters increase their temperature with climate change, stratification becomes stronger and mixing is reduced, theoretically reducing phytoplankton production. In the coastal ocean, terrestrial sources of nutrients, with their own dynamics, blur the seasonal cycle to varying degrees depending on the importance of these sources. Riverine sources, with discharge dynamics heavily modified by water use, especially around large urban areas, may alter the plankton community composition in coastal waters. Other sources of nutrients, such as atmospheric deposition, are increasingly being recognized as important, especially in the desertification scenario of the Mediterranean area (Sahara dust), but also owing to anthropogenic aerosols in an increasingly industrialized area. We will make extensive use of time series analysis of both satellite data and coastal in-situ monitoring stations to derive both seasonal signal alterations and well as long time changes, especially in chlorophyll data, and discern between open water (mostly climate related) and coastal tendencies. Chlorophyll concentration shows marginal long-time tendencies for the last 20 years but is significantly decreasing in the last few years (2013-2017), both in open waters and the coastal ocean