Le Kuai1, John Worden2, Elliott Campbell3, Susan S. Kulawik4, Meemong Lee2, Stephen A. Montzka5, Joe Berry6, Ian Baker7, Scott Denning7, Randy Kawa8, Huisheng Bian9, Yuk Yung1

Oceans are the major source in the carbonyl sulfide (OCS) global budget, emitting OCS and precursors carbon disulfide and dimethyl sulfide. Tropospheric OCS is a potential proxy to constrain changes in gross primary productivity of the terrestrial biosphere. Analysis of tropospheric OCS could provide insights into carbon-climate feedback. The spatial and temporal variation in the tropical ocean flux is still unknown and may account for a large missing source in the OCS global budget. We developed a retrieval algorithm for free tropospheric carbonyl sulfide (OCS) observations above ocean from the Aura Tropospheric Emission Spectrometer (TES). This valuable data is used in this study to constrain the ocean flux and quantify the tropical missing ocean source. The evaluation of the biases and uncertainties in TES OCS against aircraft data from the HIPPO campaigns and ground data from the NOAA Mauna Loa site suggest the TES OCS data consistent (within the calculated uncertainties 5-7 ppt) with NOAA ground observations and HIPPO aircraft measurements. This data captures the seasonal and latitudinal variations observed by in situ data. In this study, we performed a flux inversion to update the flux from TES OCS. Then we compared GEOS-Chem forward model runs with different fluxes based on TES inversion to HIPPO free troposphere estimates and NOAA near surface observations. The analysis suggests: 1) TES data supports the hypothesis that a large source from tropical ocean is missing in the current OCS global budget. 2) TES inversion implies a even larger missing source than what was estimated by Berry et al., 2013. 3) The missing source is not distributed symmetric about equator. The missing ocean fluxes are stronger at north side of equator and extend further to 40°N while are less intense and spread narrower at south side of equator ( to 20°S).

6. TES flux Inversion results

4. Validation of TES OCS• TES data has similar seasonal variations as NOAA

observations at Mauna Loa.• TES data also follows HIPPO’s latitude gradients for

five campaigns during different months of the year.• TES data consistent with both NOAA and HIPPO

observations within the estimated error of approximately 5 to 7 ppt.

1. Abstract

Email: kl@gps.caltech.edu

An evidence of tropical ocean missing source of carbonyl sulfide (OCS) by Aura Tropospheric Emissions Spectrometer (TES)

• TES data provides a strong evidence that there is a even larger missing tropical ocean source than it was previously estimated. Consequently, a missing sink may need to be explored in future study.

• Intercomparisons of OCS by three model runs to two independent observations other than TES data support the implications about the missing source by TES inversion:

- A more than 560 Gg S/yr missing ocean source is necessary but may not be as large as 1430 Gg S/yr as current TES inversion estimated. - The missing source is not symmetric about equator. It is strong and distributed further north of equator (to 40°N) but weak and narrow at south of equator (to 20°S). - TES constraints over land or at 40° to 60° over ocean for both hemispheres are still not correctly provided. So TES OCS over land is highly demanded.

Reference:

Kuai, L., et al., (2014), Characterization of Aura TES carbonyl sulfide retrievals over ocean, Atmos. Meas. Tech., 7, 163-172, doi:10.5194/amt-7-163-2014.Montzka, S. A., et al. (2004), A 350-year atmospheric history for carbonyl sulfide inferred from Antarctic firn air and air trapped in ice, J. Geophys. Res., 109, D22302, doi:10.1029/2004jd004686.Campbell, J. E., et al, (2008), Photosynthetic control of atmospheric carbonyl sulfide during the growing season, Science, 322, 1085–1088, doi:10.1126/science.1164015.Berry, J., et al. (2013), A coupled model of the global cycles of carbonyl sulfide and CO2: A possible new window on the carbon cycle, J. Geophys. Res. Biogeosci., 118, doi:10.1002/jgrg.20068.

9. GEOS-CHEM OCS to HIPPOs in free troposphere

• GEOS_apr has a tiny increase trend due to 3 Gg S/yr agreeing well with NOAA data. Amplitude of peak to peak in seasonal cycle also agrees well with NOAA observations.

• GEOS_inv1 has an unrealistic large increasing trend due to its large net source of about 1000 Gg S/yr. The seasonal cycle is too large at high latitude sites of both hemispheres. These changes are due to the changes of ocean flux between 40°S and 60°S and land flux between 40°N and 60°N by TES inversion.

• GEOS_inv2 is very similar as GEOS_apr but has a tiny decreasing trend due to its net sink of -2 Gg S/yr. Therefore OCS in this run is overall less than GEOS_apr, especially at high latitude SH sites.

1. California Institute of Technology; 2. Jet Propulsion Laboratory, California Institute of Technology; 3.University of California, Merced; 4. BAER Institute, NASA Ames; 5. NOAA Earth System Research Laboratory; 6. Carnegie Institution of Washington, Stanford; 7. Colorado State University; 8. NASA GSFC; 9. NASA Goddard Space Flight Center, USA

ObservedModel with Berry fluxes

2) Land sinks need to be increased in order to simulate a realistic seasonal cycle in NH.

3) Best hypothesis is to add a missing source over tropical ocean.

1) No obvious trend in long term observations by NOAA (red lines).

• The posterior OCS distributions agree better with TES than the priori OCS.• Bias has been removed for this inversion.

5. Flux inversion set up

Prior Inv_1 Inv_2Global annual budget (Gg S/yr)

3 998 -2

Latitude to update Kettle’s ocean flux

±40° ±60° ±20°

Method to distribute missing ocean source

Evenly distributed

TES inversion

TES inversion and scaled down by a factor of 0.75

Land flux update No Yes (TES inversion)

No

Global ocean flux 821 1692 817Missing ocean source

559 1430 555

Latitude Latitude

2. Carbonyl Sulfide Global Budget

3. Missing source hypothesis

7. Three different fluxes for forward model runs

10. Conclusions

Trend and seasonal variation in monthly mean data

• NOAA data suggests 1) three tropical ocean sites have higher OCS annual mean than other sites in both hemispheres; 2) SH OCS is higher than NH; 3) a dip feature for continental sites at N. Amer due to land uptake.

• GEOS_apr run has higher OCS annual mean at SH than both NH and tropical ocean sites. • GEOS_inv1 run has high tropical ocean OCS than NH and a big dip for N. Amer. continental sites.

However these features are amplified by TES inversion where large ocean sources are added between 20S to 40N latitude. Land flux over north part of N. Amer. and north part of Asia are scaled upward too much.

• South hemisphere sites are unrealistically high. It indicate that amplify ocean flux at 40S to 60S latitude region would remotely increase the concentrations in SH and is not realistic.

• The latitudinal gradient in GEOS_inv2 between tropical ocean and two hemispheres are getting to the correct direction but not as large as NOAA data. The dip for N. Amer. Is not deep enough.

• TES data provide the good evidence of an even larger missing source than what we previous estimate. However the constraint for high latitude region is still poorly interpreted.

Latitudinal gradient in annual mean data

• By using approximately 560 Gg S/yr total amount of missing ocean source will balance the currently global budget.

• However, by both evenly distributing the missing source within ±40° latitude region (GEOS_apr) or scale down the fluxes within ±20° latitude based on TES inversion (GEOS_inv2) can not simulate low latitude peaks as strong as HIPPO data suggested during most months.

• TES inversion estimated a much larger missing ocean source. GEOS_inv1 improves agreement with HIPPO in latitude gradient, especially two summer months when they have large gradient although the amplitudes of the peak to peak difference are overestimated by this run.

• The fluxes of both GEOS_inv1 and GEOS_inv2 based on TES inversion drive the tropical peaks to even north of equator observed in HIPPO data.

Twenty-four regions were defined by land and ocean separately for flux inversion. A scaling factor for the fluxes of each region was optimized to make OCS concentration to fit TES data better.

Latitudinal gradients in monthly mean data during four seasons

8. GEOS-CHEM OCS to NOAA observations near surface