Ocean circulation and water mass transformation beneath Filchner-Ronne Ice Shelf:Results from a 3-Docean model

Keith Makinson

British Antarctic Survey, Cambridge, U.K.

Bathymetry contours in 100’s of metres (after Nicholls and Østerhus, 2004)

FRIS sub-ice shelf circulation (OBS)

Model domain

Bathymetry Weddell Sea

Filc

hner

Dep

ress

ion

Berkner Shelf

Ronne

Dep

ress

ion

km

• MICOM with ice shelves• 0.35o grid (9 km x 9 km @ 76.5oS)• 15 isopycnic layers + mixed layer• Season surface salinity forcing• Tidal forcing• Run for 20 years

Weddell Sea

Filchner Depression

Berkner Shelf

Filchner Ice Shelf

HSSW inflow & pooling in deep depressions

Layer 16

Layer 12

Layer 15

Layerthickness

Weddell Sea

Ronne Depression

Ronne Ice Shelf Filchner Ice Shelf

How do dense water masses escape the deep depressions ?

(1) Interact with ice shelf (i.e. follow Gade line)(2) Mix with other water masses

Fox sites

SillISW

Filchner Depression – mean annual circulation

Meltwater fraction

(ppt)

Meltwater fraction

(ppt)

Filchner Depression – mean annual circulation

Filchner-Ronne Ice Front CTD sections

From Gammelsrod et al, 1994

600 m

Filchner Ice Front temperature & velocity at 600 m

oC

200 m

Filchner Ice Front temperature & velocity at 200 m

oC

800 m

Filchner Ice Front temperature & velocity at 800 m

oC

Filchner Ice Front mixing

SillISW Fox site

s

(1) Interact with ice shelf i.e. follow Gade line (2) Mix with other water masses

FilchnerIce Front

Berkner ShelfCoastal Current

600m

Meridional velocity & layer number at 77.5oScm/s

Filchner Sill Layer thickness (m)

Layer 10 velocity

FR2FR1

Meridional velocity& layer number at 75oS

cm/s

FR1FR2

FRIS sub-ice shelf circulation (Obs)

FRIS sub-ice shelf circulation (Model)

• Dense water inflows routes similar to observations

• Recirculation in Filchner Depression limited to ice front region

• Primary ISW outflow occurs on eastern side of the depression

• Convergence and mixing of water masses at Filchner Ice Front results in ISW that can escape over the sill

• The northward flow of ISW is gathered along to the eastern slope of Filchner Depression

Summary