Iceland Greenland seas Project

PI: Ian Renfrew (University of East Anglia)

CO-I’s: Tom Bracegirdle, Tom Lachlan-Cope, Alexandra Weiss

PDRA’s: Andrew Elvidge (University of East Anglia), James Pope

NERC Grant: NE/N009924/1

Project Partners: Robert Pickart (Woods Hole Oceanographic Institute), Kjetil Våge (University of Bergen), Stephanie Waterman (University of British Columbia), Kent Moore (Univesity of Toronto), Marius Jonassen (University Centre in Svalbard), Ola Persson (University of Colorado, Boulder), Guðrún Nina Petersen (Icelandic Meteorological Office) and Simon Vosper (UK Met Office)

Project Summary: The recently discovered North Icelandic Jet transports approximately half of the dense water that passes equatorward through Denmark Strait (Våge et al. 2011). This dense water contributes to the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) – the AMOC being crucial for global and European climate over a variety of timescales (Czaja et al. 2003). The discovery of the North Icelandic Jet suggests that the current paradigm for where dense water originates in the Nordic Seas is incomplete, and implicates the Iceland Sea as an undiscovered major source of dense water – one that is also being impacted by climate change (Moore et al. 2015). This has forced a redesign of our conceptual model of the ocean circulation pathways of the subpolar North Atlantic (Våge et al. 2013). However, this new paradigm is untested and the source of the North Icelandic Jet remains unknown. It has been hypothesized that relatively warm Atlantic-origin water entering the Iceland Sea is modified by air-sea interaction into dense water via convection, but it is unclear where, when or how this happens.

We will examine wintertime atmosphere-ocean processes in the Iceland Sea by characterising its atmospheric forcing, i.e. observing the spatial structure and variability of surface flux fields in the region and the weather systems that dictate these fluxes, through the first meteorological field campaign in the Iceland Sea. This will be done as part of a coupled atmosphere-ocean field campaign in winter 2017 – the first such campaign in the subpolar seas. We will make in situ observations of air-sea interaction processes from several platforms and use these to evaluate meteorological analyses, reanalyses and climate models. We will carry out numerical modelling experiments to investigate the dynamics of selected weather systems which strongly influence the region, but appear not to be well represented in many models; for example, the cold-air outbreaks that stream south over the marginal-ice-zone and densify the surface water resulting in convection; and the orographic jets and wakes that occur downstream of Iceland. We will determine what is required for atmospheric models to produce accurate surface flux fields. We will assess how the Iceland Sea is represented in current global and regional climate models and investigate likely changes in the atmospheric circulation and surface fluxes due to climate change.

We will use a range of ocean and atmospheric models to establish how current and future ocean circulation pathways function. In short, we will determine the role that atmosphere-ocean processes in the Iceland Sea play in creating the dense waters that flow through Denmark Strait and feed the lower limb of the AMOC.