A global geography of synchrony for marine phytoplankton

Abstract

Aim: Spatial synchrony in plankton is imperfectly understood yet may have far-reaching implications, for example for carbon export to the deep ocean. Several techniques have been used to describe patterns of spatial synchrony, from correlation coefficients to spectral methods. Some studies have used temporally extensive data sets to identify causes of synchrony. This study instead uses the exceptional spatial extent provided by remotely sensed data to describe, for the first time as far as we know, geographical patterns of synchrony in marine phytoplankton. We use these patterns to illuminate drivers of synchrony and of its geography.Location: The oceans. Time period: 2003-2015.Major taxon: Chlorophyll a-containing phytoplankton.Methods: Synchrony in chlorophyll a concentrations is mapped globally. Spatial statistics and model selection are used to illuminate main statistical determinants of synchrony and of geographical patterns in synchrony. Results:The first main result is that there is a pronounced and previously unmapped geography of synchrony for phytoplankton. For instance, synchrony was highest in the open ocean, specifically in gyres, and lowest in coastal regions. Spatial modelling provided the second main result that synchrony in sea surface temperature (SST) was a major statistical determinant of chlorophyll synchrony in both the Pacific and Atlantic Oceans, indicating a strong Moran effect, although possibly an indirect and/or complex one. In the Pacific Ocean, this effect depended on the time-scales on which synchrony was assessed, providing our third result, which is that synchrony of phytoplankton and its geography can be time-scale specific. Synchrony of surface solar irradiance was not associated with synchrony of chlorophyll.Main conclusions: To our knowledge, this study is the first to map geography of synchrony in marine plankton. We showed that this geography is pronounced. Geographical patterns illuminated determinants of synchrony. The geography of synchrony is a major phenomenon that has been little explored. K E Y W O R D Scospectrum, Moran effect, phytoplankton, remote sensing, spatial modelling, synchrony

The geography of spatial synchrony

“…A few prior studies have used this tool. For instance, Defriez and Reuman mapped global spatial variation in synchrony of marine chlorophyll a (Defriez & Reuman in press b ) and terrestrial vegetation (Defriez & Reuman in press a ), and used spatial statistics to infer causes of synchrony from the spatial patterns obtained. This map‐based approach is discussed in more detail in the fourth section.…”

“…A recent approach measures synchrony in neighbourhoods defined by a moving window. For each location, some metric of average synchrony among nearby locations is computed; these values are then mapped (Defriez & Reuman in press a,b ). We apply this method to 1989–1998 time series of annual peak terrestrial vegetation greenness (NDVI) derived from Advanced Very High Resolution Radiometer (AVHRR) satellite imagery for the contiguous USA (Fig.…”

“…temperature or precipitation) is driving synchrony in a biological variable through Moran effects, then synchrony maps for the driver should resemble synchrony maps for the biological variable. Similarity of maps can be tested formally using spatial statistics (Defriez & Reuman in press a,b ). This approach is similar in concept to attempts by earlier studies to attribute causes of synchrony based on similarity in patterns of distance decay between population and environmental synchrony (Koenig ; Koenig & Liebhold ), an approach that met with limited success (Liebhold et al .…”

“…The new approach is more effective because it uses detailed geographical information for inference. For instance, Defriez & Reuman ( in press a,b ) inferred drivers of synchrony in terrestrial and oceanic primary production. This approach requires data that are highly spatially resolved relative to their geographical extent.…”

A global geography of synchrony for terrestrial vegetation

“…However, our new result that geographies of synchrony in temperature and precipitation are important correlates of the geography of EVI synchrony, while true, does not follow automatically from the earlier knowledge. Defriez & Reuman () found that the geography of synchrony of incident solar irradiance was not statistically related to the geography of synchrony in chlorophyll a abundance in the world's oceans, even though it is well known that irradiance can be an important factor in chlorophyll a dynamics. In complex ecosystems, known importance of an environmental factor for ecological dynamics does not necessarily mean that the factor produces a Moran effect or a geography of synchrony, for several potential reasons, including the following: the possibility that the environmental factor itself has a muted geography of synchrony; and the possibility that the factor's influence on vegetation is nonlinear or complex in some important way that varies geographically (see, e.g., Defriez & Reuman, , where mechanisms are discussed for the phytoplankton case).…”