Variability in surface ocean DMS and isoprene in the eastern Atlantic Ocean
Christa A. Marandino1 ([email protected]), Cathleen Zindler1, Hermann W. Bange1, Eric S. Saltzman2, and Douglas W. R. Wallace1
1IFM-GEOMAR, Duesternbrooker
2UCI,
Weg 20, 24105 Kiel, Germany
Irvine, CA, 92697 USA
Introduction
Conclusion
• DMS measurements from AP-CIMS and GC-FPD in agreement regarding
DMS concentration trends over the cruise track
• There appears to be a systematic difference in the concentrations
measured using the two methods. We are currently examining the possible
reasons and hope to do more standard and instrument comparisons in the
upcoming year.
• Future laboratory tests should be performed to reduce the uncertainties
for isoprene measurements
• It is not readily apparent how the biological controls on DMS and isoprene
concentrations differ in the surface ocean. Pigments, bacterial DNA, and
bacterial productivity data from the cruise will be available in the next
months.
• Comparison of this data with aerosol load and chemical speciation will be
attempted.
• Surface seawater DMS, DMSP and isoprene were measured in the eastern Atlantic
Ocean, November 2008
• DMS, formed out of the algae metabolite DMSP, is an important precursor of remote
marine aerosols
• Isoprene, known to be emitted from terrestrial vegetation, forms secondary organic
aerosols
• Isoprene can also be produced in the ocean (e.g. Shaw et al., 2003), but the role of
phytoplankton in the production of marine isoprene and its influence on atmospheric
aerosol development has not been widely studied
• Continuous measurements were performed for DMS and isoprene with an
atmospheric pressure chemical ionization mass spectrometer (AP-CIMS)
• Discrete measurements were performed for DMS and DMSP using a purge and trap gas
chromatograph (GC)-flame-photometric detector (FPD) system
Cruise track of
ANTXXV/1 on the
R/V Polarstern
from Bremerhaven,
Germany to Cape
Town, South
Africa from 31th
October to 2nd
December 2008
Chlorophyll a concentration
50°N
in the sea surface in the
eastern Atlantic ocean
in the fourth week of
November 2008
40°N
30°N
20°N
10°N
Phytoplankton blooms
occurred along the
north west and
south west coast of Africa
0°N
10°S
20°S
30°S
Calcite concentration
50°N
in the sea surface in the
eastern Atlantic ocean
in the fourth week of
November 2008
40°N
30°N
20°N
10°N
DMS and Isoprene: Different
Biological Controls?
Elevated calcite concentrations indicate a phytoplankton bloom dominated
by coccolithophorids
0°N
10°S
20°S
30°S
1x10-2
40°S
30°W 20°W 10°W 0°W 10°E 20°E
1x10-1
1x100
1x101
1x10-4
1x10-3
40°S
mg m-3
1x10-2
1x10-1
mol m-3
30°W 20°W 10°W 0°W 10°E 20°E
DMS, DMSP and Isoprene Measurements
AP-CIMS
• DMS and isoprene were analyzed by equilibrating clean air with flowing
seawater across a porous Teflon membrane
• DMS (m/z 63) and isoprene (m/z 69) are ionized at atmospheric pressure via
proton transfer from water vapor, mass filtered via single quadrupole mass
spectrometry, and detected with an electron multiplier
Atmospheric Pressure Chemical Ionization Mass Spectrometer
Equilibrator
Ion source
Purge and Trap System + GC-FPD
•
•
DMS was transferred into gas phase by purging
filtrated seawater samples, preconcentrated in liquid
nitrogen, injected on the GC column ,and detected
with the FPD
DMSP was converted into DMS under alkaline
conditions and analyzed in the same manner as
DMS
Purge and trap system + gas chromatograph
(GC) and flame photometric detector (FPD)
Collision chamber and
high vacuum region
Purge and trap
He
strea
m
purge gas
GC-FPD
water trap
(K2CO3)
flame
photometric
detector (FPD)
Preconcenwater tration unit
ler
sampl
e
coo-
purge
unit
heater
purgin
injection on the
g
GC
gas chromatograph
(GC)
Intercomparison of DMS measurement methods
• Both instruments showed the same trend in DMS concentrations
along the cruise track
• DMS concentrations measured by AP-CIMS were systematically
higher than the FPD system
• Possible explanations:
• Increased room temperature increased the sensitivity of the FPD
• Changes in the FPD gas mixture caused a shift toward higher
sensitivity
• Calibration errors for either instrument
• Positive interferences at m/z 63 w/ AP-CIMS
• It does not appear that there was DMSP to DMS conversion in the
AP-CIMS
• DMSP variability accounts for about 28% of the DMS variability
Acknowledgements:
Thanks to the Captain and Crew of the R/V Polarstern, Cyril McCormick, the
Saltzman
Lab at UCI, and Prof. Dr. Arne Körtzinger
• Isoprene H at 25°C in seawater – no temperature dependent values
• Isoprene is very insoluble, can cause stripping in the equilibrator (data here
corrected )
• Clear difference in DMS and isoprene distributions, although both appear to
be influenced by the presence of coccolithophorids (indicated by calcite)
especially between 10°S and 30°S
• elevated DMS and DMSP concentrations coincided with increasing calcite
between 10°S and 30°S > coccolithophorid bloom is the main producer of
DMSP and DMS
• at 15°N strong increase in calcite but only weak increase in DMS and DMSP
and no influence on the isoprene concentration > possibly the age of the
algae bloom determines the production rate of these compounds
• Isoprene is clearly influenced by phytoplankton blooms, however, the main
producers are unclear
• Pigment, bacterial productivity & bacterial group type data needed to
understand biological controls
References:
MODIS data from http://oceancolor.gsfc.nasa.gov/cgi/l3?per=DAY
Shaw et al. (2003), Marine Chemistry, 80, 227– 245