NCAR Southern Ocean Workshop Sjoerd Groeskamp

10-04-2017

Could Cabbeling play a limiting role for the surface to interior pathway of Anthropogenic Carbon in the Southern Ocean?

Granite Beach, South Coast Track, Tasmania, Australia.

Mixing directions in the ocean

KH∇HC, Horizontal Mesoscale Stirring

KI∇NC, Isopycnal Mesoscale StirringD∇C, Isotropic small-scale Stirring

Water Mass Transformation Nonlinear Equation of State

Salinity

Tem

pera

ture

SmaxSmidSmin

Tmin

Tmid

Tmax

Mesoscale Mixing

Cabbeling

Simple EOS:

Reverse sign of yb

Find arguments based on Observation.Find arguments based on Observation.

Find arguments based on Observation.

Based on Observations: •WOA-2013 (S&T). •Mesoscale Mixing: —> ARGO Based:

Mesoscale mixing

Cole et al. (2015)+extrapolation

Requires Spatial Variation Eddy Diffusivity

FORMATIONAAIW

27-27.5kg/m3

Dense AAIW27.25-27.5

kg/m3

Horizontal 29 Sv 11.9

Isopycnal 4.1 Sv 8.7 Sv

Vertical -29 Sv -2.9

Surface Fluxes -26 Sv -41.2

Ongoing work.

Conclusion: Cabbeling —> important role for AAIW formation

—> Vertical (Tracer) Transport

Zonally Averaged Tendency Sea level Rise

Conclusion:

Cabbeling —> important role for AAIW formation —> Vertical (Tracer) Transport

Question:

Where is the cabbeling coming from?

Saenko and Weaver 2001: Wind Stress Applied to:

Open water and sea ice.

Open water only (=90% ice free)

Sea Ice only

Everywhere, but not to sea ice.

No AAIW formation

Abernathey et al. (2016): Ice Melt in AAIW area.From: SOSE

Their Figure 3b

Freshwater Influx from ice melt.

Warm Salty SAMW influx

Enhanced Mixing byEddies in Southern Ocean.

Cabbeling

Anthropogenic Carbon Circulation The (CA,𝝈0) Volumetric Streamfunctions

Doos and Webb (1995)Nycander et al (2006)Ferrari and Ferreira (2011)Zika et al (2012)Doos et al (2012)Groeskamp et al (2014a,b, 2016b, 2017)

Streamfunction Papers

Anthropogenic Carbon Circulation The (CA,𝝈0) Streamfunctions

Anthropogenic Carbon Circulation The (CA,𝝈0) Streamfunctions

Anthropogenic Carbon Circulation The (CA,𝝈0) Streamfunctions

1) Surface fluxes redistributed by circulation.

2) Circulation and mixing accumulate CA in AAIW range.

3) About 9 Sv of Dense AAIW formation. 4) AAIW formation important part of CA

circulation.

Question:Is cabbeling a limiting factor for CA subduction?

Schematic of resulting Circulation

Conclusions:• Cabbeling significant for AAIW formation (Nycander et al 2015,

Groeskamp et al 2016).

• Anthropogenic Carbon subducted with AAIW

• Anthropogenic Carbon accumulating in the AAIW region.

Questions:• If Sea Ice melt creates S&T contrast that allows for AAIW, what happens

when sea-ice flux changes?

• Is there a seasonality in AAIW formation?

• How does the AAIW formation influence subduction of tracers and specifically Anthropogenic Carbon.

Mixing in the ocean

Conclusions/Future Work (1/3)•Cabbeling significant for AAIW formation.

•Streamfunction for Tracer-Tracer coordinates.

•Applied to S&T to understand water mass transformation and heat and salt transport (and mixing).

•Applied to CA and 𝝈0, to understand CA accumulation and redistribution.

•In this model: •TW: Uptake = Loss.

—> Large CA transport: from TW to SAMW. •CA Accumulation: —> Mostly SAMW/AAIW. •AAIW: Important for surface -> Interior CA transport. •S.O. Eddies: Important for surface -> Interior CA transport. •NADW: Small but DEEP surface -> Interior CA transport. •AABW not so much.

Diapycnal Redistribution:Transport and Accumulation

TW to SAMW Eddies and Seasonal Cycle

NADW

Diapycnal Redistribution:Transport and Accumulation