DEEP BASIN. INNER. MID-SHELF. JEFFREY’S LEDGE. UNH R/V Gulf Challenger. Kennebec- Androscoggin Rivers. Portland ME. UNH & PMEL CO2 coastal buoy at 65 m depth. WB2. Portsmouth NH. WB7. UNH Monthly Wilkinson Basin Transect. Merrimack River. Boston MA.
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UNH R/V Gulf Challenger
Kennebec- Androscoggin Rivers
UNH & PMEL CO2 coastal buoy at 65 m depth
UNH Monthly Wilkinson Basin Transect
Monthly sampling of pCO2 vs. 3-hourly buoy sampling
As shown on the map at far left, UNH has a buoy moored just east of WB2 collecting pCO2 data using the NOAA/PMEL MAP-CO2 system. The buoy has been deployed since 2006 and data below are being used to assess hourly to daily variations in the surface layer air and sea CO2 levels. The range of daily buoy-observed variation about ship monthly-interpolated is significant, but the general agreement with that estimate is striking as well. The combined cruise and buoy data are being used to assess future sampling strategies for the wider Gulf, as well as the study of storm and discharge events.
Coastal Buoys NDBC/GoMOOS/UNH
Flo-thru oxygen, IOPs and CTD
2007-2008 - 12 months
+0.02UNH/PMEL MAPCO2 buoy
+0.17Monthly ship data
Examination of interannual ocean CO2 and air-sea CO2 flux in the Western Gulf of MaineDouglas Vandemark1, Joseph Salisbury1, Jim Irish1, Christopher Hunt1, Shawn Shellito1, Fei Chai21University of New Hampshire 2University of Maine Contact: [email protected]
ΔpCO2 Time Series and Air-Sea Flux Variations 2004-2008
One benefit of the repeated cross-shore transects is their utility for examining and monitoring the seasonal and inter- annual cycles within this coastal ecosystem. Figures below illustrate a portion of our composite data set with the focus being station WB2 using monthly ship + supporting nearby station data to retrieve a bulk air-sea CO2 flux.
Multi-year air-sea CO2 flux estimates – all stations
Hourly estimates of the CO2 air-sea flux are computed using the UNH cruise data and the nominal procedure for hourly mass flux estimation given as:
FCO2 (molC/m2/hr) = α* kw(U) * (ΔpCO2)(1)
where α is the gas solubility (a known quantity of T and S), kw the bulk gas transfer coefficient, and ΔpCO2 = [pCO2seaside] – [pCO2airside], pCO2 being the gas’ partial pressure at 1 atm. kw is estimated hourly with several algorithms (e.g. Wanninkhof, 1992; Wanninkhof and McGillis, 1999) – each in terms of an hourly or ‘steady’ 10m neutral stability anemometer wind speed. While atmospheric CO2 measurements are typically collected aboard the Challenger we use a locally-modeled (see Padin et al., 2007) level for the airside level due to substantial (10-30 ppmv) daily variations that can limit their use is a one-per-month ΔpCO2 estimate in the first panel shown at left. Temperature, salinity and pCO2 data are interpolated from monthly values onto a 1 hour time step grid to estimate fluxes using Eq. 1.
5 yr average
Net annual air-sea flux estimates 2004-2008
Inshore, Mid, and Offshore Stations
A Carbon Source, but…
While the Gulf is a productive ecosystem, our 5 year time series is showing the surface waters to be a weak net source with 2004 being the strongest year. But 2005-6 years were near neutral in C flux. The maximum annual swing for this region occurs between 2005 and 2004, amounting to a -1.1 TgC difference when averaged across the relevant area of the Gulf of Maine.
Wanninkhof 1992 with hourly NDBC winds
01 m depth
50 m depth
Fig 1 - Map of study region in the Western Gulf of Maine, and coastal shelf divisions (lower panel) versus depth and distance from the coastline for the cross-shore Wilkinson Basin transect – a single day cruise executed monthly since April 2004.
Note the addition of the UNH/PMEL CO2 time series station near WB2 starting in May 2006.
The Kennebec/Androscoggin river system is a key landward influence upon the Western Gulf 4 where surface flow is predominantly North-South.
Hourly estimate (monthly ship pCo2)
Monthly avg., ~5 yr climatology
Hourly-to-Daily Ancillary Data - Chlorophyll_a, Salinity, River Discharge
Buoy 44030 -
03 m depth
SeaWiFS - daily
01 m depth
50 m depth
Five river average (USGS)
Thanks to all members of the R/V Challenger data collection team, GoMOOS and U. of Maine (N. Pettigrew and C. Roessler), NDBC, and to Drs. Jim Irish and Janet Campbell. This work was supported in part by the NOAA Coastal Services Center through an award to the UNH Center for Coastal Ocean Observation and Analysis (COOA); NOAA award NA16OC2740.
RARGOM Gulf of Maine Symposium
St. Andrews-by-the-Sea, New Brunswick October 4-9, 2009