1. Seasonal Evolution Of Dissolved Inorganic Carbon Along A Cross-shelf Transect In The Gulf Of Maine: The Influence Of Riverine Discharge.
Joe Salisbury (UNH)
Doug Vandemark (UNH)
Janet Campbell (UNH)
Chris Hunt (UNH)
Amala Mahadevan (BU)
Bror Johnsson (BU)
Wade McGillis (LDEO)
Huijie Xue (UMO)

2. Questions
What are the time and space scales of inorganic carbon distributions in a temperate coastal regime?
Are the temporal dynamics of biologically-mediated DIC different in plume and oceanic provinces?
Ancillary climate change questions---

3. Outline:
Setting
Data and Methods
Results
Conclusions

4. - UNH monthly transects (right)
Coastal Ocean Observation and Analysis Center (COOA) Gulf of Maine and associated watersheds (left) UNH COOA Transects (right)
Monthly sampling since April 2004 of Western Gulf of Maine out to depth of 400 m.
CoIs are Vandemark, Salisbury, Morrison, Campbell, Runge, Bucklin
Objectives include space/time variability of pCO2 and net ecosystem metabolism as well as riverine influence on the Gulf

5. The Spring and Summer of 2005 were really wet
Mean surface salinity (Apr-July, 04)
Mean surface salinity (Apr-July, 05)

6. Measurements of the COOA time series
Measurements used in this project

7. UNH Field Component R/V Gulf Challenger
Profilers for IOPs , AOPs, and CTD
Infrared CO2 gas analyzer
Fast-rate CO2 equilibrator
Flo-thru pCO2, oxygen, IOPs, GTD, and CTD

8. Spatial variability in continuous measurements

9. Methods:
Along each cruise track, estimate DIC and biologically-mediated DIC (DICbio) for cruises during 2004 and 2005.
Within the domain, estimate volumes of freshwater and oceanic influence.
Plot data in space-time grids
Estimate spatio-temporal distribution of DICbio, net DICbio accumulation (source/sink term) and temporal derivative of DICbio (related to NEM).
- Underlying assumption - day-scale processes can be attributed along isohalines. e.g. For any day, “measured” DICbio is consistent along the entire isohaline.

10. Estimate of DICbio DICbio
DIC estimated from “conservative” alkalinity and atmospheric pCO2
DICbio
Observed DIC - estimated from measured DIC (or alkalinity) and pCO2

11. Estimate of plume volume (all water <32psu)
a) Estimate of plume area using GOM-POM model
b) Estimate of plume depth (interpolated from cruise profiles)
5/19/04
5/21/05
14 m
c) depth * area = volume (km3)

15. Estimated dissolved inorganic carbon (DIC) mol kg-1
Discharge 103 ft3 s-1

16. - mainly a dilution signal from low DIC river water
DIC mixing anomaly (mol kg-1) due to salinity and temperature
- mainly a dilution signal from low DIC river water

17. Biological DIC anomaly (DICbio mol kg-1)*
note: - Difference between years
Across track variability
Temporal derivative related to ecosystem production*

18. Average DICbio (mol kg-1) in plume and non-plume volumes

19. Average daily net DICbio production (mmol C m2 day-1)*
Plume
Non-plume
* Calculated as (7-day derivative) / 7

20. )
Plume
Non-plume
Total

21. Conclusions:
In terms bio-mediated CO2, this system is variable in time and space, alternately changing between a local source and sink of atmospheric CO2 on monthly time scales.
Over 20 months of observations, our domain was a very small sink of CO2 (-120 mtC, but ranged from to mtC over the time series.)
The freshwater from the land apparently affects the net surface productivity (different time signatures in plume and non-plume regions)
Use caution when making budgets from limited time series. e.g a lot different than 2005
Suggestive of sensitivity to minor climate variations.