Introduction to marine primary productivity and carbon cycle
Satya Prakash [email protected] 400 Law Dome Ice Core, Antarctica 380 Mauna Loa, Hawaii
Slope: 360 1970 - 1979: 1.3 ppm y-1 -1 340 2000 - 2006: 1.9 ppm y
320 Concentration (ppm) 2
CO 300
280 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020 Year CO2 – Temperature Relationship
CO2 Concentration Temperature 380 4 2 340 0 300 -2 (ppmv) 2 260 -4 Degree C Degree
CO -6 220 -8 180 -10 0 50 100 150 200 250 300 350 400 450
Age (Kyr)
VOSTOK Ice Core data How much is 100 ppm??
1 ppm = 2.12 * 1015 gm = 2.12*109 tonnes 100 ppm = 2.12 thousand crore tonnes
1m. 1m.
= 1000 kg = 2.44 टन 1m. CO2 1m. Water or one tonne 1m. 1m. Partition of Anthropogenic Carbon Emissions into Sinks [2000-2006]
45% of all CO2 emissions accumulated in the atmosphere
55% were removed by natural sinks Ocean removes ~ 24% Land removes ~ 30% Upper Photic Layer
Photosynthesis
O2 O2
CO2 CO2 Respiration
Deeper Aphotic Layer The Ocean
Euphotic zone light - ~little N
Aphotic zone no light - lots N
Photosynthesis is a process that generates the organic matter in phytoplankton cells.
The process of photosynthesis can be represented as: hv
106CO2 + 122H2O + 16HNO3 + H3PO4 (CH2O)106(NH3)16H3PO4 + 138O2 Available solar energy in the waveband 400-700 nm.
This reaction illustrates the need for the nutrients: nitrate and phosphate. It also shows that for every 106 CO2 molecules taken up, approximately 138 O2 molecules are produced. Primary production is the rate of synthesis of organic material from inorganic compounds such as CO2 and water. It is significant as it provides the base of most of the entire marine food chain.
The formation of organic carbon compounds from inorganic carbon (e.g. carbon dioxide) involves a reduction reaction; the reducing power) comes from either the absorption of light (photosynthesis), or the oxidation of other compounds (chemosynthesis).
It is a rate, hence involves dimensions of time: mg C m-3 d-1, or in a depth integrated sense, mg C m-2 d-1 The Biological Pump • Plankton grow, mature and die—taking carbon with them to the deep ocean
• They have a larger effect on climate than any single other process or group of organisms
• 99% of marine life relies on plankton—they form the base of the marine food chain.
•About 10% of the carbon fixed by photosynthesis in the surface layer, escapes this layer by sinking into the deep ocean. This flux is called New Production or Export Production. phytoplankton need:
light
CO2 nutrients water
In the ocean, light and nutrient availability may limit the rate of photosynthesis. THE MAJOR FORESTS IN THE SEA ARE PHYTOPLANKTON Major Nutrients
- 2- + • Nitrogen (NO3 , NO4 , & NH4 ) –Limiting in marine systems 3- • Phosphorus (PO4 ) –Limiting in freshwater systems
• Silica (SiO2) –Important to diatoms • Redfield ratio 106 : 15 : 16 : 1 C Si N P Nutrient sources to surface waters are: rivers and land runoff upwelling atmosphere
The most productive regions of the oceans are the coastal regions because this is where upwelling is strongest and where river and land runoff meet the sea. Here nutrients result in high productivity rates, which in turn result large fisheries. Regions with upwelling represent the productivity
Equatorial upwelling
Coastal upwelling
Water turbidity
Components of primary production
Total Production = New production + Regenerated production
New Production Regenerated Production Ammonium Urea
Photic Photic Zone Nitrate Recycling
New Production is defined Regenerated Production is as production due to newly uptake of recycled borne nitrate into surface nutrients such as layer ammonium and urea
f-ratio = New Production / Total Production New Production ~ Export production Excess nutrients Excess aquatic plants
Fish kills
Dead plants decay
Low dissolved oxygen Vertical distribution of Nutrients Photic Zone and Compensation Depth Biomass Nutrients Photosynthesis Irradiance Intensity
Ik
Z (meters) Atlantic & Pacific nutrient and oxygen distribution Sources and sinks of dissolved Oxygen
Sources: Physical exchange between atmosphere and Ocean, mainly diffusion By product of photosynthesis
Sinks: Community respiration Bacterial degradation of organic matter Leads to formation of oxygen depleted zone in the sub-surface layer (100 – 1000m) Dissolved Oxygen in Sub-surface water
Oxygen profiles in the Northern Indian Ocean
Major Oxygen minimum zones around the world’s Ocean. A map showing the annual mean dissolved oxygen levels at a depth of 200 m. Source: Levitus Climatology Oxygen Minimum Zone
Oxygen Minimum Zones (OMZs) are the intermediate-depth layers characterized by very low oxygen concentrations
OMZs occur in regions of low dynamical supply and high demand of oxygen
i.e., in regions of low ventilation by subsurface currents and productive upwelling systems, where intense biological uptake of oxygen associated with bacterial respiration and remineralisation occur [Resplandy et al., 2012]
Low oxygen levels have dramatic implications for the ecosystem, coastal environment, and economics In the Indian Ocean, OMZs are found in both the Arabian Sea (AS) and the Bay of Bengal (BoB)
The Arabian Sea OMZ (ASOMZ) is the second most-intense OMZ of the world ocean and is usually observed between 100-m and 1000-m depths, with oxygen concentrations less than or equal to 20 μmol/L
The oxygen concentrations in BOBOMZ are more or less constant
------
Oxic Zone : Region in where dissolved oxygen is abundant (O2 more than 100 µmol/kg) Hypoxic zone : A typical threshold for hypoxic zone is approximately 60 µmol/kg (~10- 60μm/kg) Suboxic zone : The suboxic zone is defined as a region which experience nitrate reduction but not sulphate reduction (Suboxic range : O2 < 2-10 µmol/kg)
Anoxic zone : region which experience complete depletion of oxygen and are a more severe condition of suboxia (~0μm/kg) ------Nitrogen Cycle N2
Nitrification - PON NH + NH OH NO - NO3 Oxic 4 2 2 Suboxic - - NO2 NO3 Denitrification Remineralisation
- NO2 Organic N NO
N2O
Anammox + N NH4 2 Climate Change and Dissolved Oxygen
Global Surface Warming Heating Less Upwelling
Increased Less Ventilation Stratification
Less export production Reduction in supply from Increase in surface residence time of deeper water Less Oxygen demand
Decrease in O2 inventory in the sub-surface/deeper layer What are the controllers on Export Production?
If macronutrients are unavailable then the
CO2 flux is reduced! Nitrogen appears to be the most important controlling factor that limit the primary productivity of ecosystems.
1) Ocean nutrient inventory
2) Utilization of nutrients in HNLC condition
3) Change of Redfield Ratio What is “HNLC”?
• High Nutrients Low Chlorophyll • Mainly in Southern Ocean, Equatorial and sub- Arctic Pacific Ocean • First defined by Minas et. al 1986 as a region having potential for high production but lower observed productivity • Several hypothesis have been proposed to explain this condition HNLC regions of World Ocean
HNLC Hypothesis to explain HNLC Condition 1. Low specific growth rates • Nitrate and phosphate concentrations are 2. Low temperature high year round but standing stocks of phytoplankton are always low (0.2-0.4 µg/L; 3. Deep mixed layer normal yield is 1 µg /L) 4. Grazing hypothesis • Iron concentrations in these waters are sub- nanomolar: the same as those that are 5. Fe limitation known to limit growth of phytoplankton, particularly large species such as diatoms. • Addition of low levels of Fe promotes growth of large phytoplankton. -bottle experiments -in situ fertilization experiments
Different Iron experiments done so far Redfield ratio (stoichiometry carbon, nitrogen and phosphorus in phytoplankton.
Redfield (1963) described the remarkable congruence between the chemistry of the deep ocean and the chemistry of living things in the surface ocean (i.e. phytoplankton). Both have N:P ratios of about 16. When nutrients are not limiting, the molar element ratio C:N:P in most phytoplankton is 116:16:1. Redfield thought it wasn't purely coincidental that the vast oceans would have a chemistry perfectly suited to the requirements of living organisms.
He considered how the cycles of not just N and P but also C and O could interact to result in this match. Figure 13.8
Modern Time
N2 fixation
De-nitrification
N = 25790 N* = N – 16 P
Redfield Ratio of 16:1 for particulate organic matter is an upper bound for N:P in the dissolved inorganic phase.
Today’s ocean has an average dissolved inorganic N:P ratio of ~14.7:1
Implies an imbalance between nitrogen fixation and denitrification
•CO2 exchange is dependent on limiting nutrient Ratio of nitrogen fixation to denitrification is crucial to CO2 •Dissolved inorganic nitrogen exchange limits productivity Nutrient flux and dead zones: correlated??
Increase of Nitrogen influx into river
Distribution of dead zones in the world Excess nutrients Excess aquatic plants
Fish kills
Dead plants decay
Low dissolved oxygen UNCE, Reno, NV The biggest concern with excess nutrients is eutrophication
Results in: • impacts on lake/stream ecology webs; • toxins; • drinking water treatment problems; • other changes in lake chemistry How global warming affects ocean productivity? Effects of Climate Change on Oceans
1. Melting sea ice, stratification
2. Warming –productivity-changes in community structure
3. Precipitation regimes-nutrient transport from the landLong- eutrophication time series are needed to get a clear 4. Ocean acidification picture
Schematic model illustrating the effect of sea-surface warming on upper-ocean processes in low (Upper) and high (Lower) latitudes. Graph depicts the effects on stratification and mixed-layer depths, nutrient supply (yellow arrows), plankton biomass, and particle flux (green arrows).
Source: Riebesell, Kortzinger and Oschlies , PANS, 2009 The Efficiency of Natural Sinks: Land and Ocean Fractions
• Part of the decline is attributed to up to a 30% decrease in the efficiency of the Southern Ocean sink over the last 20 years. • This sink removes annually 0.7 Pg of anthropogenic carbon. • The decline is attributed to the strengthening of the winds around Antarctica which enhances ventilation of natural carbon-rich deep waters. • The strengthening of the winds is attributed to global warming and the ozone hole.
Canadell et al. 2007, PNAS Trends in global ocean chlorophyll: 1997-2003
In most central ocean gyres, chlorophyll concentrations decreased between 1997 and 2003
McClain et al., DSRII, 2004
Declines in mid-ocean gyres chlorophyll associated with increases in sea surface temperature
Gregg et al., GRL, 2005 Trends in global ocean chlorophyll: 1997-2007
Trend in monthly anomalies of SeaWiFS-derived chlorophyll concentration (top panel) and primary production (bottom panel) for the period September 1997–December 2007.
Only points where the trend is statistically significant at the 95% level are plotted. Black contours and large numbers denote the 14 biomes. The biomes are designed to reflect very large-scale contrasts in primary productivity.
The trends in the sub-tropics have been interpreted as reflecting the impact of global warming
Source: Henson et al., Biogeosciences, 2010 Trend in surface chlorophyll in western Arabian Sea : 1997-2003
Is this hypothesis true for the entire Arabian Sea or is just a local phenomenon?
Source: Goes et al., Science, 2005 Arguments and counter-arguments!!!!
• Satellite data shows that summer productivity in the western Arabian Sea has been increasing
• Warming of the Eurasian land mass – the melting of the Himalayan snow cover – increase in land–sea contrast in summer temperature – strengthening of monsoon winds
• Gregg et al., 2005, who first reported change in productivity did not attribute it to the global warming
• Whenever the southwest monsoon weakened (e.g. at the last glacial c. 21,000 years ago), the northeast monsoon strengthened and vice versa (e.g.,Duplessy et al.,1982)
• If arguments proposed by Goes et al., 2005 are taken in accordance with the palaeo-climate data, one would expect a decreasing trend in the winter productivity in the northeastern Indian Ocean. Is there any trend in the Eastern Arabian Sea?
(a) Chlorophyll from SeaWiFS data from 1997-2005 (b) SST from AVHRR and MODIS
Source: Prakash and Ramesh 2007 Trends in global ocean chlorophyll: 1997-2006
global Monthly anomalies in global (depth > 15oC integrated) Chl for 1997-2006 reveal two highly Significant trends: 1. rise in Chl which corresponds to the 1997 to 1999 El Nino to La Nina transition 2. Decline in Chl from 2000-2006
These trends are particularly true for region having SST >15Cm marked by black line in figure below
Source: Behrenfeld et al., Nature, 2006 Basin Averaged Chlorophyll data analysis
Source: Prasanna Kumar et al., Current Science, 2010 Is there any trend for the entire Arabian Sea?
Area averaged monthly time-series of SeaWiFS derived Chl-a for the Arabian Sea basin (45 to 80E & 0 to 25N) for years 1997–2010.
Chl for 1997-2010 reveals two highly significant trends:
1. rise in Chl which corresponds to the 1997 to 1999 El Nino to La Nina transition
2. No change since 2000 in basin average Chl
Source: Prakash et al., GRL, 2012 Source: Prakash et al., GRL, 2012 Is there any change in the wind over the region?
Time series of area averaged monthly wind speed by CCMP (black, solid line), Quick Scat (blue, long dash), TMI (green, short dash) and monthly wind stress Curl (X 107) for the region R4 for years 1997–2009 (red bar). Trends lines fitted to individual data are also shown in the same color of time series. TMI wind data has been plotted for the period of 1997–2003 (following Goes et al. [2005]); Slopes of the trend lines are insignificant (up to two decimal places). Source: Prakash et al., GRL, 2012 Change in trends in the Western Arabian Sea?
2.0
1.5
1.0
0.5
0.0 97 98 99 00 01 02 03 04 05 06 07 08 09 10 Year Area averaged monthly time series of Chl-a for the region R4
Weekly SSHA in the western Arabian Sea during the third week of August for years 1997–2010. Box represents region R4. The presence of a cold core eddy, marked by negative SSHA, can be clearly seen in year 2003. Source: Prakash et al., GRL, 2012 What governs the observed change?
a). Area averaged monthly time series of sea level anomaly (blue) and thermocline depth (D23- red) along with their trends for the region R4 during 1997-2010.
b). Area averaged monthly time series of TMI SST for the region R4. Trend lines shows decrease (slope = -0.17) from 1998-2003 and increase (slope = 0.10) from 2003 onwards in the minimum SST.
Source: Prakash et al., GRL, 2012 THANK YOU for your attention
Satya Prakash [email protected] [email protected] Annual aeolian dust input（gm–2yr–1） (Jickells et al., 2005) Fixation
N2 Nitrification Mineralization NH Uptake NO3 4
Phytoplankton Mix Layer Grazing depth Chlorophyll Zooplankton Mortality Large Water column Susp. detritus particles Continental shelf sediments are responsible for up to 67% of marine N Nitrification denitrification N2 NH estimates 4 NO3 De-nitrification Aerobic mineralization Sediment Organic matter De- -, resulting in the formation of nonbiologically available N, primarily N2 gas