Abstract
Abstract. Like other inland seas, the Caspian Sea (CS) has been influenced by climate change and anthropogenic disturbance during recent decades, yet the scientific understanding of this water body remains poor. In this study, an eco-geographical classification of the CS based on physical information derived from space and in situ data is developed and tested against a set of biological observations. We used a two-step classification procedure, consisting of (i) a data reduction with self-organizing maps (SOMs) and (ii) a synthesis of the most relevant features into a reduced number of marine ecoregions using the hierarchical agglomerative clustering (HAC) method. From an initial set of 12 potential physical variables, 6 independent variables were selected for the classification algorithm, i.e., sea surface temperature (SST), bathymetry, sea ice, seasonal variation of sea surface salinity (DSSS), total suspended matter (TSM) and its seasonal variation (DTSM). The classification results reveal a robust separation between the northern and the middle/southern basins as well as a separation of the shallow nearshore waters from those offshore. The observed patterns in ecoregions can be attributed to differences in climate and geochemical factors such as distance from river, water depth and currents. A comparison of the annual and monthly mean Chl a concentrations between the different ecoregions shows significant differences (one-way ANOVA, P < 0.05). In particular, we found differences in phytoplankton phenology, with differences in the date of bloom initiation, its duration and amplitude between ecoregions. A first qualitative evaluation of differences in community composition based on recorded presence–absence patterns of 25 different species of plankton, fish and benthic invertebrate also confirms the relevance of the ecoregions as proxies for habitats with common biological characteristics.
Highlights
The Caspian Sea (CS) is an enclosed water body that plays an important geopolitical role in the Central Asia region (Kosarev and Kostianoy, 2005)
Using names according to their geographical characteristics, we found five of the distinguished ecoregions in the northern Caspian Basin (NCB) (NCB River Outflows (NCB-RO), NCB Western Shelf (NCB-WS), NCB Ural Furrow (NCB-UF), NCB Easternmost Shelf (NCB-ES) and NCB Transition (NCB-T)), three in the middle Caspian Basin (MCB) (MCB Transition (MCB-T), MCB Coastal (MCB-C) and MCB Offshore (MCB-OS)) and two in the southern Caspian Basin (SCB) (SCB Coastal (SCB-C) and SCB Offshore (SCB-OS))
Ecoregions in the NCB are smaller in size than those identified in the two other basins
Summary
The Caspian Sea (CS) is an enclosed water body that plays an important geopolitical role in the Central Asia region (Kosarev and Kostianoy, 2005). During the last few decades, the joint action of natural and anthropogenic factors has been aggravating the environmental state in the CS (Kopelevich et al, 2004; Barale, 2008). Increasing human activities such as the oil and gas industries, especially in the northern part of the CS, fisheries, agriculture and tourism (Kopelevich et al, 2004), together with decades of environmental mismanagement (Barale, 2008), have led to the severe degradation of water quality. The CS ecosystem has recently been shown to change drastically over timescales of several decades (Shiganova et al, 2004, 2010, 2011; Karpinsky et al, 2005), with massive impacts on plankton and fish biomass, chlorophyll a Published by Copernicus Publications on behalf of the European Geosciences Union
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.