Marine Ecosystems and Interdecadal climate variations Vidyunmala V. Ph.D Student, CAOS

Overview ● Introduction to oceanic ecosystems ● Influences of oceanic ecosystems ● Results from Sea-Wifs ● Summary

Oceans and Climate: Ocean waters continuously move around the globe like a process which is running on conveyor belt. Factors that control this movement are 1. wind 2. saltiness of water and 3. temperature Oceans take up large amounts of carbon dioxide and effect the climate on long-term

Oceanic ecosystems: Phytoplanktons are single celled plants which live in the surface waters of the ocean. They use sunlight, water and carbon dioxide in a process called photosynthesis and gives oxygen which is the living source for other organisms. The two major nutrients required for phytoplanktons to grow are; nitrogen and phosphorous. Remineralisation: Phytoplankton grow very quickly only living for a day or so, when they die they are eaten by bacteria or zooplankton which convert their organic matter back into carbon dioxide, release the nutrients they have used and use back oxygen. This process is called remineralisation.

Gases from Phytoplankton and their effect on climate : Phytoplankton's produces a chemical called Dimethyl sulphoniopropionate, the breakdown of this chemical releases dimethyl sulphide (DMS). When phytoplankton are eaten or dead or infected, DMSP release into the seawater where they form DMS, Much of this emission stays in seawater as food for bacteria and a portion of it enters the atmosphere. DMS when entered the atmosphere has two effects 1. Direct effect 2. Indirect effect

Gases from Sea-water: ✔ Gases from sea -water can be mainly divided into two groups: ✔ Affecting the lower troposphere ✔ Affecting the stratosphere Halocarbons - Halocarbons are organic compounds containing halogen atoms. One of the important marine halocarbons is Methyl Iodide. They are formed by sea-weeds and some species of phytoplankton, They can react with sunlight and form chemicals which are more toxic than CFCs.

Methane (CH4) – Methane is a major greenhouse gas which is both natural and man-made. When oxygen concentration in the water is zero, then bacteria generates methane when they eat organic matter. It can also be produced by the action of heat and pressure on burried organic matter. In coastal waters, eutrophication is a problem, in such cases methane amounts to the atmosphere will rise. Non-methane Hydrocarbons- Hydrocarbons are a group of organic compounds containing hydrogen and carbon. NMHCs are more in land than in oceans. NMHC's are produced biologically and by the action of sunlight on organic matter. One of the most important NMHC's is isoprene. NMHCs once escape into the air are highly reactive with ozone.

Nitrous oxide - Nitrous oxide is another important biologically produced gas. It has a very long life time in the troposphere around 120 years. Estuaries and coastal waters are the important source regions. Here, nitrous oxide is produced by bacteria converting nitrogen compounds into nutrients. Nitrous oxide is 275 times more powerful greenhouse gas than carbon dioxide. In stratosphere, it reacts with sunlight to form NO radicals which affect ozone. Carbonyl Sulphide (COS) – Carbonyl sulphide is the major sulphur gas which enters in the atmosphere. Marine derived carbonyl sulphide is formed by the action of sunlight on sulphur-containing organic matter in the upper layers of the ocean, particularly in coastal waters. It doesnt dissovle easily in sea-water so enters the atmosphere. It will be converted to sulphate aerosols in the stratosphere and thus reflect back solar energy.

How do we approximate the Phytoplankton data ● Chlorophyll-a is the primary photosynthetic pigment contained in almost all plants. ● Phytoplankton grow and reproduce when they get enough nutrients, carbon and light. ● Chl-a provides information on primary production and subsequent assessment of secondary and higher order production processes such as zooplankton.

How is the phytoplankton derived from a satellite data ? ● Ocean water containing very little particulate matter, scatters light as a Rayleigh Scatterer with bluish color of the ocean. ● Photosynthetic pigment Chl-a found in phytoplankton absorb higher energy blue light but reflect green light. ● Thus as the concentration of phytoplankton increases ocean color shifts from blue to green.

How does the Ocean-biology effect the Pacific Inter-decadal Climate Variability? Previous studies by Miller et al (2003), reviewed that there are two prominent theories to explain pacific interdecadal climate variability. (1) subduction mode hypothesis, (2) Midlatitude Gyre mode and the influence of ocean biota in these hypothesis. The mid-latitude SST anomalies can be altered by biological feedbacks including phytoplankton radiation and absorption and local DMS effects and CCN formation etc., I t It can affect in two ways, (i) the amplitude of SST may be altered by phytoplankton radiation absorption effect, (ii) the atmospheric response which completes the gyre mode feedback, ie.., DMS effects the clouds and the flow of energy and so on.

Hence, the equatorial region is a key area requiring atttention. Large incident solar radiation, Strong atmospheric response to SST anomalies in the tropics The key question to address is: Seasonal variation of these Chl-a distribution and its relation to ENSO or Indian ocean dipole situation.

Summary :

Reference: Miller et al., Potential Feedbacks between pacific ocean ecosystems and interdecadal climate variations, BAMS, May 2003, vol.84,

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