Rapid ocean acidification in the Sub-Arctic Deep Sea and the Diversity of Benthic Molluscs

Chair: Victoria Cole

Hronn Egilsdottir(1,2), Jon Olafsson(1,2), Niall McGinty(3,4), Gudmundur Gudmundsson(5)

1 Institute of Earth Sciences, University of Iceland, Reykjavik, 101, Iceland
2 Marine Research Institute, Reykjavik, 121, Iceland
4 Mathematics and Computer Science, Mount Allison University, New Brunswick, Canada
5 Icelandic Institute of Natural History, Gardabaer, 212, Iceland

Background
Deep sea ocean acidification (OA) and the ecological consequences thereof have received little attention in the scientific literature to date. The main reason is the inaccessibility of the deep sea and the costs involved with sample collection. This is regrettable as deep sea organisms are predicted to have limited capacity for acclimatization. Molluscs are both common and functionally important in benthic ecosystems but also highly vulnerable to decreasing ocean pH and calcium carbonate saturation (ΩCaCO3). Studies on biodiversity patterns in relation regional hydrography are crucial for predicting future impacts of OA and warming.

Methods
The Greenland-Iceland-Scotland Ridge is a topographic barrier between the Arctic Iceland Sea and the Subpolar North Atlantic south of Iceland. We compare the temporal variation in hydrography and carbonate chemistry between these areas using data collected for over 30 years at two time series stations. We also compare the depth distribution, species richness and biodiversity of benthic molluscs in these areas by using data collected during the benthic sampling program BIOICE (1992 to 2004) which contained 1390 samples from 590 stations at depths ranging from 20-3000 meters around Iceland.

Findings
There is a strong contrast between the study areas in terms of temporal hydrographic variability with high rates of change observed in the Iceland Sea where the Ωaragonite=1.0, Ωaragonite=1.1 and Ωaragonite=1.2 horizons are shoaling at a rate of 6, 8 and 13 meters per year respectively. Species richness and diversity of bivalves and gastropods decreased more strongly with depth in the Iceland Sea compared to the area south of Iceland. We identify abundant taxa and relate to their life history and functional traits.

Conclusions
The findings of this study are discussed in the context of ecosystem resilience in the Arctic Nordic Seas and the rates of change observed throughout the water column in this region.