Seasonal variability of stable carbon isotopes (δ¹³C_DIC) in the Skagerrak and the Baltic Sea : Distinguishing between mixing and biological productivity

Summary, in English

We documented the annual cycle of the carbon isotopic composition of dissolved inorganic carbon (δ¹³C_DIC) in the water columns of the Skagerrak and Baltic Sea to obtain an increased understanding of the processes involved controlling the carbon isotopic distribution in shelf seas. The lowest δ¹³C_DIC values (-4.9‰) were found in the low-oxygen, brackish Baltic bottom water whereas the highest values (+1.8‰) were observed in the surface water of the Skagerrak during late summer. Photosynthesis drove the high δ¹³C_DIC values (between 1.0 and 1.8‰) noted in the surface waters of both the Skagerrak and the Baltic. The δ¹³C_DIC values below the halocline in the Baltic reflect mixing of brackish water and the more saline water from the Skagerrak, and foremost organic matter remineralization processes that release significant amounts of low-δ¹³C CO₂. Similarly, in the stagnant fjord basins, little deep water exchange and the degradation of terrestrial and marine organic matter set the δ¹³C composition. Deep-water renewal in the fjord basins resulted in rapid increases of the δ¹³C_DIC on the order of 1‰, whereas remineralization processes caused a decrease in δ¹³C_DIC of 0.1-0.3‰ per month depending on location. The combined effects of water mixing and remineralization processes (estimated using apparent oxygen utilization (AOU) values) yielded the expression: δ¹³C_DIC =0.032*S-0.01*AOU-0.12 for the Baltic - Skagerrak region at water depths below the halocline.

• Author: Helena L. Filipsson; Daniel C. McCorkle; Andreas Mackensen; Joan M. Bernhard; Lars S. Andersson; Lars Johan Naustvoll; Angela M. Caballero-Alfonso; Kjell Nordberg; Didrik S. Danielssen
• Department/s: Department of Geology; BECC: Biodiversity and Ecosystem services in a Changing Climate
• Publishing year: 2017-10
• Language: English
• Pages: 15-30
• Publication/Series: Palaeogeography, Palaeoclimatology, Palaeoecology
• Volume: 483
• Links: http://dx.doi.org/10.1016/j.palaeo.2016.11.031
• Document type: Journal article
• Publisher: Elsevier
• Topic: Oceanography, Hydrology, Water Resources; Geosciences, Multidisciplinary
• Keywords: Anoxia; AOU; DIC; Estuary; Hypoxia; Time-series
• Status: Published
• Project: Vi behöver slipa proxy verktygen - stabila isotoper med höägre prestanda för bättre paleoceanografisk modellering; Lund University Centre for studies of Carbon Cycle and Climate Interactions
• ISBN/ISSN/Other: ISSN: 0031-0182