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Contributions from the Peruvian upwelling to the

tropospheric iodine loading above the tropical East Pacific

H Hepach 1* , B. Quack 1 , S. Tegtmeier 1 , A. Engel 1 , J. Lampel 2,6 , S. Fuhlbrügge 1 , A. Bracher 3 , E. Atlas 4 , and K.

Krüger 5

* hhepach@geomar.de

Affiliations

1 GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Germany

2 Rosenstiel School of Marine and Atmospheric Science (RSMAS), University of Miami, USA

3 Alfred-Wegener-Institute (AWI) Helmholtz Center for Polar and Marine Research, Bremerhaven and Institute of Environmental Physics, University of Bremen, Germany

4 Institute of Environmental Physics, University of Heidelberg, now at Max Planck Institute for Chemistry, Mainz, Germany

5 now at Scripps Institution of Oceanography, University of California San Diego, USA 6 Department of Geosciences, University of Oslo, Norway

References

Carpenter, L., MacDonald, S., Shaw, M. D., Kumar, R., Saunders, R. W., Parthipan, R., Wilson, J., and Plane, J. M. C.:

„Atmospheric iodine levels influenced by sea surface emissions of inorganic iodine“, Nature Geoscience, 2013.

Engel, A. and Galgani, L.: „The organic sea surface microlayer in the upwelling region off Peru and implications for air-sea exchange processes“, submitted to Biogeosciences 2015.

Fuhlbrügge, S., Quack, B., Atlas, E., Fiehn, A., Hepach, H., and Krüger, K.: „Meteorological constraints on oceanic halocarbons above the Peruvian Upwelling“, submitted to Atmos. Chem. Phys. 2015.

Hepach, H., Quack, B., Fuhlbrügge, S., Raimund, S., Tegtmeier, S., Bracher, A., Atlas, E. L., Engel, A., Galgani, L., and Krüger, K.: „Contributions of biogenic halogenated compounds from the Peruvian upwelling to the tropical troposphere“, in preparation.

Ocean Surface Microlayer workshop, Kiel, July 1 – 3 2015

INTRODUCTION

Biological processes

CH

3

I, CH

2

I

2

, CH

2

ClI

I

y

(e.g. IO)

+O

3

aerosol, ultra-fine particles, HOx and NOx chemistry, ozone chemistry

CONCLUSIONS AND OUTLOOK

RELATIONSHIP TO BIOLOGICAL PARAMETERS M91-CRUISE

Fig 3: Cruise track for M91 with SST in the color coding. Four upwelling regions (roman numerals) were identified.

• Callao, Peru to Callao, Peru, December 1 to 26 2012

• Four upwelling regions (see Sea Surface Temperature – SST)

Fig. 4: dCCHO and TUra measurements directly from the microlayer (upper panel) along with measurements of CH3I and CH2ClI in the subsurface (around 6.8 m).

Spearman‘s rank

correlation

CH

3

I CH

2

ClI CH

2

I

2

dCCHO

ULW

TUra

ULW

Diatoms 0.73 0.79 0.72 0.68 0.75

TUra

ULW

0.83 0.88 0.52 0.94

dCCHO

ULW

0.82 0.90 0.55

CH

2

I

2

0.66 0.59

CH

2

ClI 0.83

Table 1: Spearman‘s rank correlation coefficients rs of the three iodocarbons with DOM constituents in the subsurface (dCCHOULW – dissolved polysaccharides, TUraULW – total uronic acids) and diatoms.

Suggested production pathway:

(release Haloperxidases)

DOM

(polysaccharides, uronic acids)

+ IPO / photochemistry (IPO – iodoperxidase)

CH

3

I, CH

2

I

2

, (CH

2

ClI)

Photolysis

CH

2

ClI

The accumulation of DOM in the sea surface in regions of high iodocarbons (Fig. 3) suggests potential production of these compounds in the very surface with direct link to the air-sea interface.

RESULTS FROM THE CRUISE POSSIBLE CONTRIBUTION TO IO

RV Meteor

Fig. 5: Iodocarbons in sea surface water (upper panel), the lower troposphere (lower panel), along with a map of Chl a (see color bar).

Fig. 7: Sea-to-air fluxes of iodocarbons

Fig. 6: Gradient of virtual temperature E-2 along with the height of the Marine Atmospheric Boundary Layer (MABL) (black – derived from ozone sondes, blue – derived from multiple linear regression)

• Mean (max) CH

2

ClI – 10.9 (58.1) pmol L

-1

, CH

3

I – 9.8 (35.4) pmol L

-1

, CH

2

I

2

– 7.7 (32.4) pmol L

-1

 very elevated, lead to enhanced fluxes (Fig. 7)

• Large atmospheric mixing ratios: CH

2

ClI – 0.4 (2.5) ppt (lifetime: few hours), CH

3

I – 1.5 (3.2) ppt (lifetime: few days), CH

2

I

2

– 0.2 (3.3) ppt (lifetime: few minutes)

• Distribution of longer lived atmospheric CH

3

I also strongly influenced by MABL heights (high when MABL is low, low when

MABL is high) (Fig. 6)

Fig. 8: Contribution of emissions of

organoiodine combounds to measured iodine oxide (IO) with different fractions.

IO [ppt ] IO [ppt ]

I

-

HOI

Fig. 1: Iodine in the ocean with photochemical production of CH3I and biological production of CH3I, CH2I2 and CH2ClI contributing to the tropospheric iodine (Iy) loading, with HOI and I2 as additrional inorganic source for Iy.

Outlook: The sea surface microlayer represents a potentially very significant source for iodocarbons due to its unique DOM composition, with direct contact to the air-sea

interface. This will be investigated during the ASTRA cruise to the Peruvian upwelling in October 2015.

I

2

I

-

DOM

Research: How does the tropical, very biologically active Peruvian upwelling contribute to the tropospheric iodine loading of the tropical East Pacific? Which factors contribute to the regional

distribution of oceanic and tropospheric CH

3

I, CH

2

I

2

and CH

2

ClI?

CH

3

I, CH

2

I

2

, CH

2

ClI

I

y

(e.g. IO)

+O

3

HOI, I

2

DOM

(polysaccharides, uronic acids) IPO DOM

DOM

SML

 CH

3

I, CH

2

I

2

, CH

2

ClI MABL

Fig. 2: Conclusions and outlook from the M91 cruise. Purple indicates conclusions, green indicates the outlook.

Tradewind inversion

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