BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Andrea Rochner (University of Exeter) DTSTART:20210407T130000Z DTEND:20210407T140000Z DTSTAMP:20260423T021423Z UID:BAS-PO/14 DESCRIPTION:Title: Contemporary Southern Ocean CO2 flux variability in the UKESM1 and ocean-o nly simulations\nby Andrea Rochner (University of Exeter) as part of B AS Polar Oceans Seminar\n\n\nAbstract\nThe Southern Ocean is a strong cont emporary sink for atmospheric CO2 due to the interaction of various driver s\, including strong winds\, biological activity\, or the overturning of w ater masses and their carbon content. A fundamental question is whether th e Southern Ocean will continue taking up similar proportions of CO2 in the future. However\, future projections are hampered by the large uncertaint y in contemporary CO2 fluxes in Earth System Models (ESMs) and result from differences in individual model set-ups and their representation of CO2 f lux drivers\, historically sparse observations\, and gaps in the understan ding of the regional distribution and natural variability of air-sea CO2 f lux.\n\n \n\nIn this talk\, I will first introduce some of the open questi ons and challenges for both observations and models with regard to the CO2 flux in the Southern Ocean. I then explore the CO2 flux and its drivers i n the Southern Ocean for the fully-coupled historical UK Earth System Mode l (UKESM1) simulation\, compared to simulations using the UKESM1’s ocean component forced with reanalysis data. The comparison highlights several shortcomings in the UKESM1 simulations. Differences in the phase of the se asonal cycle of net CO2 flux appear between the simulations: while the sea sonal cycle is out of phase with observations in the UKESM1\, the ocean-on ly simulation is in phase. This phase change is related to differences in the underlying physical processes\, namely upper ocean stratification\, wi nter mixed layer depth in the sub-Antarctic region\, and circulation\, whi ch occur in response to the different atmospheric forcing. Disagreements i n the timing of the seasonal cycle are not uncommon for ESMs\, as are bias es in the named physical processes. The results described here may therefo re be valid for a larger group of ESMs. However\, there are features of th e CO2 flux which do not improve or even exacerbate despite improved physic s representation in the ocean-only run\, such as the magnitude of the CO2 flux or the decadal variability. The results thus illustrate the complexit y of simulating the Southern Ocean CO2 flux\, current limitations and oppo rtunities for future model developments.\n LOCATION:https://researchseminars.org/talk/BAS-PO/14/ END:VEVENT END:VCALENDAR