Adequacy of the Argo array for monitoring water mass changes in the

Gulf Stream's northern recirculation gyre Denis Gilbert Institut Maurice-Lamontagne Pêches et Océans Canada Mont-Joli, Québec

Argo Science Workshop 3 Hangzhou, China, March 26, 2009

OUTLINE

•  Argo seen from a coastal perspective •  Isopycnal analysis: T-S-O2 fields • Winter mixed layer depth • Dynamic height •  Some thoughts on the design of Argo array

Modified from Shaw et al. (2002, QSR)

Deep ocean climate affects waters far inland

Argo float territory

Warm-core rings (WCR)

8-day composite satellite imagery of SST on 06/11/1997 (Chauduri et al. 2009, Cont. Shelf Res. 29: 393-406)

Water properties

on the 27.25 kg/

m3 density surface

Gilbert et al. (2005, L&O, 50: 1654-1666)

T

O2

S

O2 sat.

Historical T-S-O2 data from ISDM and NODC databases (1914-2003)

Water mass mixing: NACW – LCW

1931-1935 72% LCW, 28% NACW

1980-2003 53% LCW, 47% NACW

Gilbert et al. (2005, L & O, 50: 1654-1666)

Water mass mixing: LCW – NACW

28%

72%

53% 47%

Labrador Current Water

North Atlantic Central Water

In the 1930s, deep waters (300 m) in the St. Lawrence Estuary were •  colder •  fresher •  more oxygenated

From 1984 to 2008, deep waters (300 m) in the St. Lawrence Estuary were •  warmer •  saltier •  less oxygenated

Labrador Current Water (LCW) and North Atlantic Central Water (NACW)

147 µM

Gilbert et al. (2005), Limnology and Oceanography, Vol. 50: 1654-1666.

Slope Water region (depth > 2000 m for Argo)

Expected number of floats in Slope Water •  Slope Water region (d > 2000 m) has an area of

650 000 km2. •  For a target float density of one float per 90000

km2 (300 km x 300 km ), we should thus have an average of 7 floats in the Slope Water region.

•  Same calculation using a density of 3ºlatitude x 3ºlongitude (85000 km2) gives an average of 8 floats in the Slope Water region.

Number of Argo floats in Slope Water

Target Argo density is 7.5

Number of profiles from Argo floats in 2007 1/3° latitude x 1/2° longitude grid is chosen to help "capture" the LCW signature

Time window for 1/3° latitude x 1/2° longitude • One year of Argo data leaves too many

empty "squares". • Need to focus on multi-year instead of

single-year analyses. • Next slides consider 1998 to 2007 period,

using Argo data only.

Depth of σθ= 27.25 kg m-3 isopycnal

Gilbert and Nault (2008)

Temperature on σθ= 27.25 kg m-3

Gilbert and Nault (2008)

Salinity on σθ= 27.25 kg m-3

Gilbert and Nault (2008)

Gilbert et Nault, AZMP Bulletin PMZA, 2008

Temperature and salinity anomalies

Dynamic height anomaly relative to 1000 db

Some thoughts on the Argo array

Could CTD sampling on shelf help with DMQC?

Gilbert and Nault (2008)

Could CTD sampling on shelf help with DMQC?

Gilbert and Nault (2008)

Winter mixed layer depth

Proposed changes to Argo design

• Rather than using a uniform 3ºx3º float density coverage, promote finer (coarser) spacing in regions with smaller (larger) spatial correlation scales.

•  Improve float density coverage for better monitoring of boundary currents.

•  Improve linkages with shelf monitoring programs (CTD shelf transects, gliders…)

SUMMARY

•  At the original Argo design density of one float per 3º, we can expect an average of 7 or 8 floats to be present in the Slope Water region.

•  The present Argo design allows the study of climate variability over time scales of pentads (5 years), but is insufficient for studying interannual variability.

Argo trajectories - Howard Freeland

http://www.pac.dfo-mpo.gc.ca/sci/osap/projects/argo/trajmovies_e.htm