Equatorial Indian Ocean Process Study Dynamics and Biogeochemistry (EIOPS)

Transcription

1 Equatorial Indian Ocean Process Study Dynamics and Biogeochemistry (EIOPS) Submitted to INCOIS Ministry of Earth Sciences Government of India Hyderabad 31 January

2 Title of the project: Equatorial Indian Ocean Process Study - Dynamics and Biogeochemistry Principal Investigator: S. Prasanna kumar Scientist National Institute of Oceanography Dona Paula Goa Proposal submitted to: Director INCOIS Ministry of Earth Sciences Govt. of India Hyderabad 31 January

3 1. Executive Summary Equatorial oceans are special regions of World Ocean where the air-sea coupling is most intense, and hence plays an important role in climate regulation. The Equatorial Indian Ocean (EIO) is distinct from the equatorial regions of Pacific and Atlantic, because of its seasonality in the zonal wind and currents and lack of equatorial upwelling. In spite of this unique characteristic, our understanding of EIO is rudimentary primarily due to lack of in situ data. Still meager is the availability of co-located simultaneous observation on physical and biogeochemical parameters which are essential to understand the EIO processes and will have bearing to climate regulation. Recently convened international SIBER (Sustained Indian Ocean Biogeochemical and Ecological Research) workshop, at Goa in October 2006, also expressed the need for such measurements which are in line with the IGBP programme such as IMBER (Integrated Marine Biogeochemistry and Ecosystem Research). It is in this context that the present proposal is conceived. The broad goals of the Equatorial Indian Ocean Process Study Dynamics and Biogeochemistry (EIOPS) are to: 1. Examine the ocean-atmospheric processes that cause and maintain mixed-layer and barrier layer in the Equatorial Indian Ocean. 2. Study the role of upper ocean processes in regulating the chlorophyll and biological productivity of the EIO on a seasonal and intraseasonal scale. 3. Understand the biogeochemistry of the EIO and its impact on regional CO 2 balance. The proposed programme envisages collection of high-resolution in situ physical and biogeochemical data along two trans-equatorial section, 77 o E and 83 o E, from 5 o N to 5 o S during 4 seasons namely, spring intermonsoon, summer, fall intermonsoon, and winter. In addition, the archived CTD data and ARGO data will also be made use of. Additionally, remote sensing data on chlorophyll pigment concentrations, SST, SSH anomaly and sea surface winds will also be used. Apart from the observed data (both in situ as well as remote sensing) a state-of-the-art ocean biogeochemical model will be 3

4 employed to address the issues related to biogeochemistry of the EIO. The proposed project period is 4 years. This is a multi-institutional programme in which researchers from National Institute of Oceanography (NIO), Goa, Indian National Centre for Ocean Information Services (INCOIS) Hyderabad, and University of Maryland, USA will collaborate to achieve the project goal. 2. Background Equatorial oceans are special regions of World Ocean where the air-sea coupling is most intense, and hence plays an important role in climate regulation. Unlike the Equatorial regions of Pacific and Atlantic, the zonal wind stress as well as zonal currents in the Equatorial Indian Ocean (EIO) exhibits semi-annual cycle (Knox, 1976, Luyten and Roemmich, 1982). The current in the EIO reverses from the westward flowing North Equatorial Current during boreal winter (November to February) to the eastward flowing Indian Monsoon Current during boreal summer (June to September). During spring (April to May) and fall (October to November) intermonsoons a very strong current known as Wyrtki Jet (Wyrtki, 1973, Han et al, 1999) flows eastward which is narrow as it is equatorially trapped (Knox, 1976, Reverdin and Luyten, 1986). Another distinction of EIO is that an undercurrent is found only during boreal winter (Taft and Knauss, 1967; Leetmaa and Stommel, 1980) and there is no equatorial upwelling. Of the three equatorial regions of the world ocean, EIO is the least studied primarily due to the lack of in situ data. Most our understanding of EIO is based on very few observations such as International Indian Ocean Expedition (IIOE) during (Wyrtki, 1971), time-series measurements near Addu Atoll at Gan (Knox, 1976), Indian Ocean Experiment (INDEX) during ( ) (Leetmaa and Stommel, 1980), Surface Indian Ocean Dynamic Experiment (SINODE) during (Reverdin and Luyten, 1986), and ship drift data (Cutler and Swallow, 1984). There were also efforts to understand the dynamics of EIO through modeling (Reverdin, 1987 and references there in; McCreary et al., 1993; Han et al., 1999; Murtugudde et al., 1998 & 2000, Murtugudde and Busalacchi, 1999; Prasanna Kumar et al., 2005). 4

5 With the advent of remote sensing technique in oceanography, the data availability improved. The recent discovery of Indian Ocean Dipole (IOD) (Saji et al., 1999; Vinayachandran et al., 1999, Murtugudde et al., 1999) kick started new enthusiasm in the Indian Ocean research by way of sustained observation such as equatorial mooring (JAMSTEC, PMEL, and NIO) and continuation of XBT lines which will improve our understanding of the EIO (see for e.g., Sengupta et al. 2004) as well as the effect of ENSO and IOD as an element of climate variability. In recent years an increasing body of evidence is emerging which indicates that oceanic ecosystem and hence the ocean biogeochemistry exert an influence on the physical climate system directly (radiative transfer processes in the upper ocean) as well as indirectly (alteration in the concentration of CO 2 ). However, sustained co-located and simultaneous measurements of physical and biogeochemical parameters to understand such processes and climate variability do not exist at the moment. Recently convened international SIBER (Sustained Indian Ocean Biogeochemical and Ecological Research) workshop at Goa during October 2006 (Raleigh Hood and Naqvi, 2006) also focused on the need and urgency of such measurements which are in line with the IGBP programme such as IMBER (Integrated Marine Biogeochemistry and Ecosystem Research, see It is in this context that the present proposal is conceived. 3. Objectives Overall goals of the Equatorial Indian Ocean Process Study Dynamics and Biogeochemistry (EIOPS) are to: 1. Examine the ocean-atmospheric processes that cause and maintain mixed-layer and barrier layer in the Equatorial Indian Ocean. 2. Study the role of upper ocean processes in regulating the chlorophyll and biological productivity of the EIO on a seasonal and intraseasonal scale. 3. Understand the biogeochemistry of the EIO and its impact on regional CO 2 balance. 5

6 4. Implementation plan As a part of the process study, the proposed programme envisages collection of high resolution in situ physical, chemical and biological data along two cross-equatorial transects on a seasonal time scale. In addition to the in situ shipboard measurements, available hydrographic data from CTD and ARGO will be used along with remote sensing data on chlorophyll pigment concentrations, sea-level height anomaly, sea surface temperature and wind to meet the project objective. Apart from the observed data (both in situ as well as remote sensing) efforts will be made implement a state-of-the-art BGC model to study the biogeochemical response of the northern Indian Ocean including EIO to seasonal and sub-seasonal scale processes. 4.1 Data collection and analysis To meet the project objectives, in situ measurements will be carried out to cover 4 seasons as detailed in the table. Depending on the availability of ship time efforts will be made to collect as much data as possible so as to cover all the seasons. Number Season Period Preferred period for measurement 1 Spring Inermonsoon March-May April 2 Summer monsoon June- July-August September 3 Fall Intermonsoon October October 4 Winter monsoon November- February December-January 4.2 Area of Study and Station location The study domain is the Equatorial Indian Ocean from 50 o N to 5 o S. Two high resolution (half-a-degree stations from 3 o N to 3 o S and one-degree stations north of 3 o N and south of 3 o S) trans-equatorial sections along 77 o E and 83 o E were selected for in situ measurements of physical and 6

7 biogeochemical parameters. There are 21 CTD stations and 5 PP (Primary Productivity) stations along each transect. These transect along 77 o E and 83 o E were selected because two deep-sea current meter mooring is deployed at (1) equator and 77 o E deployed since September 2003 and (2) equator and 83 o E deployed since December PP Stations CTD Stations NIO Mooring 77E 2003 September 83E 2000 Dec Fig.1 Station location for in situ measurements 7

8 4.3 Parameters to be measured Shipboard CTD will be operated up to 1000m depth and using Rosette sampler water samples will be collected for analysis of physical, chemical and biological parameters. Surface currents along the track will be measure using shipboard ADCP while surface meteorological parameters will be measured along the track using shipboard automatic weather station. 14 C based primary productivity will be measure in situ on moorings while new production will be based on 15 N. All the measurements will be based on JGOFS protocol (UNESCO, 1994). 1. Temperature profile 2. Salinity profile 3. Sea surface temperature (SST) 4. Wind speed and direction 5. Air temperature and wet bulb temperature 6. Atmospheric pressure 7. Current speed and direction (ADCP) 8. Chlorophyll a C based Primary production rate N based new production 11. Phytoplankton 12. Mesozooplankton 13. Microzooplankton 14. Bacterial abundance 15. Dissolved oxygen 16. TCO2 17. ph 18. Alkalinity 19. Nitrate 20. Phosphate 21. Silicate 4.4 Biogeochemical Modelling activities Dr. Raghu Murtugudde, Associate Professor of University of Maryland, USA, has agreed to be a collaborator who will help to set up regional configurations of 2 different models (ESSIC-BOGCM and ROMS) for the Indian Ocean domain (30E-110E, 25S-30N) including river discharges and the ITF (Indonesian Through Flow) represented as a sponge layer and the open boundaries in the south will also be sponged. The surface heat fluxes will be computed by coupling the models to an advective atmospheric mixed layer so that the non-local effects of atmospheric humidity and air temperatures will be properly represented especially for computing SST and SSS accurately to capture their impact on air-sea exchanges of CO2. Iron limitation is explicitly modelled in the ESSIC-BOGCM whereas ROMS at present does not have iron limitation. Horizontal and vertical resolutions will 8

9 be chosen appropriately to represent the mixed layer-thermocline interactions and their impact on surface ecosystem responses and model-data intercomparisons. Since the focus will be on the deep tropical and North Indian Ocean, the impact of ITF will be neglected in this configuration but a coarser resolution Indo-Pacific version of the ESSIC-BOGCM will be run to explore the ITF influence on the nutrient and ecosystem variability in the study region. The main thrust will be to understand the physical variability, as observed from the cruises and from all available ancillary data such as satellites and VOS and CLIVAR repeat hydrography cruises, and the interaction between the environmental changes in the ecosystem response and the biogeochemical variability in the Indian Ocean. Impacts of dynamical forcing due to winds and thermodynamical variability induced by surface fresh water and heat fluxes will be separated with sensitivity studies. The contrast between the Arabian Sea, the Bay of Bengal, and the equatorial eastern and western regions will be of particular interest with specific focus on seasonal and inter-annual contrasts and the primary, new, and export productions and role of diurnal mixed layer variability and inter-region interactions. Phasing of each of the sub-regions in response to ENSO and IODZM will be placed in the context of leading modes of climate variability vs the leading modes of biogeochemical responses. 4.5 Collaborators Dr. Balakrishnan Nair Indian National Centre for Ocean Information Services (INCOIS) Ministry of Earth Sciences, Govt. of India Ocean Valley, P.B. No.21, IDA Jeedimetla P.O Hyderabad bala@incois.gov.in Dr. Raghu Murtugudde Associate Professor ESSIC/DAOS, CSS Bldg, Room 2201, University of Maryland, College Park, MD 20742, USA. Ph: (301) , FAX: (301) ragu@essic.umd.edu 9

10 5. Budget (Rupees in lakhs) S.N Items Amount (Rs in lakhs) 1 Equipments (GoFLO samplers, computer/laboratory 10.0 furniture) 2 Computing facilities ( Workstation, PCs, Laptops, and peripherals, and AMC) Chemicals & consumables (including spares for DOC 16.0 analyzer spares, Plakton Nets, PP mooring hardware, etc 4 Contingency TA & DA Domestic *International 6 Manpower (4 PA-III + I JRF + 1 Postdoc fellow) 30.0 Total 94.0 * 4 visits of a foreign expert(s) and 4 visits of NIO scientists are envisaged. For carrying out 4 cruises, personnel, equipment and material needs to be moved from Goa to place of embarkation and from place of disembarkation back to Goa. Major portion of TA is needed towards this. Contingency amount is needed for paying the shipping bills and associated cruise expenditure. Amount for Ship-Time S.N Items Amount (Rs in lakhs) 1 Ship time of 28 days each for lakhs per day Total = 654 lakhs 10

11 6. Duration & Time schedule: 4 years Time schedule Recruitment of project personnel Procurement of PP mooring hardware, equipments and spares etc In situ Data collection and analysis Biogeochemical Model set up and run Report preparation and publications Q1& Q2 Q3& Q4 Q1& Q2 Q3& Q4 Q1& Q2 Q3& Q4 Q1& Q2 Q3& Q4 7. Milestones New knowledge on the mechanisms of generation and maintenance of equatorial mixed-layer and barrier-layer on a seasonal scale and heat exchange processes within the upper ocean and thermocline. New insight on the regulation of biological productivity of EIO by physical processes. Knowledge on the impact of EIO Biogeochemistry on the regional and global CO 2 balance in relation to climate variability/change. 8. Deliverables Generation of high-resolution (spatial) temperature, salinity, nutrients, chlorophyll profile data together with other chemical and biological parameters from the equatorial Indian Ocean on a seasonal scale. Scientific publications in SCI journals. 11

12 Establishment of biogeochemical modeling capability. Establishment of High degree of collaboration among the institutions within and outside the country. References Cutler, A., and Swallow, 1984: Surface currents of the Indian Ocean (to 25 o S, 100 o E): compiled from historical data archived by the meteorological office, Bracknell, UK, Institute of Oceanographic Sciences, Rep.No.187, 8pp. & 36 charts. Han, W., McCreary, J.P., Anderson, D.L.T., Mariano, A.J., 1999: Dynamics of the eastward surface jets in the equatorial Indian Ocean. J. Phys. Oceanog, 29(9), Hood, R.R., and S.W.A. Naqvi, 2006: SIBER Workshop, 3-6 October 2006, Goa, India. IMBER New Letter, 5, 1-3. Knox, R.A., 1976: On a long series of the Indian Ocean equatorial currents near Addu Atoll. Deep-Sea Res., 23, Leetma, A. and H.Stommel, 1980 : Equatorial current observations in the western Indian Ocean in 1975 and J. Phys. Oceanog., 10, p Luyten, J.R. and Roemmich D.H., 1982 : Equatorial currents at semiannual period in the Indian Ocean. J. Phys. Oceanog., 12, p McCreary, J.P., P.K. Kundu and R.L. Molinari, 1993 : A numerical investigation of dynamics, thermodynamics and mixed-layer processes in the Indian Ocean. Prog. in Oceanog., 31 (3), Murtugudde, R., A.J. Busalacchi and J. Beauchamp, 1998: Seasonal to Interannual effects of the Indonesian throughflow on the tropical Indo- Pacific basin. J. Geophys. Res., 103 (10) Murtugudde, R., S. Signorini, J. Christian, A. Busalacchi, and C. McClain, 1999: Ocean color variability of the tropical Indo-Pacific basin observed by SeaWiFS during J. Geophys. Res., 104, 18,351-18,

13 Murtugudde, R., and A. Busalacchi, 1999: Interannual variability of the dynamics and thermodynamics of the tropical Indian Ocean. J. Clim., 12, Murtugudde, R., J. McCreary, and A. Busalacchi, 2000: Oceanic processes associated with anomalous events in the Indian Ocean. J. Geophys. Res, 105(C2), Prasanna Kumar, S., A. Ishida., K. Yoneyama, M.R. Ramesh Kumar, Y. Kashino, H. Mitsudera, 2005: Dynamics and thermodynamics of the Indian Ocean warm pool in a high-resolution global general circulation model. Deep-Sea Res. II, 52, Reverdin, G., J. Luyten, 1986 : Near-surface meanders in the equatorial Indian Ocean. J. Phys. Oceanog., 16 (16), p Reverdin, G. 1987: The Upper Equatorial Indian Ocean: The climatological seasonal cycle, J. Phys. Oceanog, 17 (7), Taft, B., and J.Knauss, 1967: The Equatorial Under Current in the western Indian Ocean as observed by the Lusiad Expedition. Bull. Scripps Inst. Oceanogr., 9. Saji NH, Goswami BN, Vinayachandran PN, Yamagata T, 1999: A dipole mode in the tropical Indian Ocean. Nature, 401(6751), Sengupta, D., Retish Senan, V.S.N. Murty and Vijayan Fernando, 2004: A biweekly mode in the equatorial Indian Ocean. J. Geophys. Res., 109, C10003, doi: ,2004jc Vinayachandran, P. N., N. H. Saji, and T. Yamagata., 1999 : Response of the equatorial Indian Ocean to an unusual wind event during Geophys. Res. Lett., 26 (11) p UNESCO Protocols for the Joint Global Ocean Flux Study (JGOFS). Manual and Guides 29, pp