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SUMMARY:Sophie Meyjes - Impact of global variability in zooplankton grazin
 g rates on carbon export flux - Joshua Lanham - Regimes of seasonal CDW in
 trusion onto the circumpolar Antarctic shelf in a high-resolution model  -
  Sophie Meyjes (University of Cambridge) and Joshua Lanham (University of 
 Cambridge)
DTSTART:20231019T103000Z
DTEND:20231019T113000Z
UID:TALK206962@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:Sophie Meyjes - Impact of global variability in zooplankton gr
 azing rates on carbon export flux\n\nThe biological carbon pump is a key c
 ontroller of how much carbon is stored within the global ocean. This pathw
 ay is influenced by food web interactions between zooplankton and their pr
 ey. In global biogeochemical models\, Holling Type functional responses ar
 e frequently used to represent grazing interactions. How these responses a
 re parameterised greatly influences biomass and subsequent carbon export e
 stimates. The half-saturation constant\, or k value\, is central to the Ho
 lling functional response. Empirical studies show k can vary over three or
 ders of magnitude however\, this variation is poorly represented in global
  models. This study derives zooplankton grazing dynamics from satellite ob
 servations\, resulting in global distribution maps of the grazing paramete
 r k. The impact of these spatially varying k values on plankton biomass an
 d carbon export flux estimates is then considered. This study finds large 
 spatial variation in k values across the global ocean\, with distinct dist
 ributions for micro- and mesozooplankton. High half-saturation constants a
 re generally associated with areas of high productivity. Grazing rate para
 meterisation is found to be critical in reproducing satellite-derived dist
 ributions of nanophytoplankton biomass\, highlighting the importance of to
 p-down drivers for this size class. Locally optimised grazing dynamics mod
 ifies total carbon export by >16%\, with increases in faecal pellet export
  and decreases in export from algal aggregates. This study highlights the 
 importance of grazing dynamics to both community structure and carbon expo
 rt\, with implications for modelling marine carbon sequestration under fut
 ure climate scenarios.\n\nJoshua Lanham - Regimes of seasonal CDW intrusio
 n onto the circumpolar Antarctic shelf in a high-resolution model \n\nBasa
 l melting of Antarctic ice shelves is driven by heat delivery from Circump
 olar Deep Water (CDW). However\, the mechanisms and routes of CDW inflow t
 o the shelf are often uncertain. The formation of Dense Shelf Water (DSW) 
 at the ocean-ice interface is thought to be a key factor in modulating the
  amount of CDW that can cross the shelf break. Coarse resolution climate m
 odels struggle to explicitly resolve DSW due to its highly localised forma
 tion areas. We classify water masses using an optimum multiparameter (OMP)
  analysis in an eddy-resolving formulation of MITgcm (SOHI). The analysis 
 successfully reproduces the key features of the known near-shelf water mas
 s configuration\, including the sites of DSW formation. We identify five m
 ajor circumpolar regimes of seasonal CDW intrusion on the shelf. The East 
 Antarctic shelf region is largely characterised by a seasonal CDW cycle wh
 ich is directly driven by the strength of the along-slope easterly winds. 
 In West Antarctica\, CDW concentrations on the shelf are primarily determi
 ned by the strength of the undercurrent\, which is itself mediated by the 
 seasonal strength of westerly winds associated with the Amundsen Sea low p
 ressure system. Shelf regions of DSW production either show no significant
  CDW seasonality\, or exhibit a CDW cycle which is an inverse of the cycle
  of DSW production. The distinction between these two regimes appears to b
 e determined by shelf geometry. Finally\, we find that shelf-ward CDW infl
 ow can occur along the western edge of canyons during periods of DSW overf
 low. 
LOCATION:Open Plan Area\, Institute for Energy and Environmental Flows\, M
 adingley Rise CB3 0EZ
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