SIO 101. California Coastal Oceanography Lecture 4: Chemicals that support biological production
Alvarez-Salgado et al. 2006
Reading: Martz et al. (2014). Dynamic variability of biogeochemical ratios in the Southern California Current System, Geophys. Res. Lett. 10.1002/2014GL059332 Oct. 13th 2020 Chemicals of Interest For Biological Production
- -1 Nitrate ( NO3 ): 0 to 40 μmol L (μM; micromolar)
3- -1 Phosphate (PO4 ): 0 – 2.5 μmol L (μM)
-1 Silicate (SiO4): 0 to 40 μmol L (μM)
-1 Dissolved inorganic carbon (DIC, includes CO2): 1900-2200 μmol L (μM)
-1 Oxygen (O2): (0) 50-250 μmol L (μM)
+ -1 Ammonium (NH4 ): 0-3 μmol L (μM)
Micronutrients, e.g., iron (Fe): pico to nanomolar
- Do you expect NO3 and O2 to vary in a similar manner? Nutrient samples and basic water properties are collected using a CTD-Rosette Do Phytoplankton in the California Current Ecosystem Region (CCE) Adhere to the “Redfield Law?”
Martz et al., set out to examine this.
35 km 250 km
However, in Martz et al., high frequency measurements were made in-situ What is this Redfield Law?
REDFIELD RATIO (average in phytoplankton):
(CH2O)106(NH3)16(H3PO4) + 138O2 ó106CO2+ 16HNO3 + H3PO4 + 122H2O Concepts Introduced in the Martz Paper
Upwelling redistributes elements essential for biological production
Gas exchange alters upwelling “signature”
Why the focus on nitrate?
Redfield ratio f-ratio
What do ratios of upwelling nutrients tell us about all of the above? What is the vertical structure of the nitrate profile in the CCE? (June 2017)
- Nitrate Concentration [NO3 ] µM 0 10 20 30 40 50 0 What drives 100 Nitrate the shape of this profile? 200
300 Why isn’t it 400 always zero at the surface?
Depth (m) Depth 500
600 Santa Typical 700 Barbara deep Basin water 800 profile 900 Inshore and offshore profiles of dissolved nitrate, phosphate and silicic acid
Concentration (µM) Concentration (µM) -10 -10 0 5 10 15 20 0 5 10 15 20
10 10
30 30
Phosphate 50 50 Silicic Acid Nitrite Nitrate 70 70 Ammonium Depth (m) Depth Depth (m) Depth 90 90 Phosphate Silicic Acid 110 110 Nitrite Nitrate 130 Ammonium 130
150 150 Coastal Upwelling Delivers Nutrients to the Surface Ocean
Contours: Nitrate (μM N)
Upwelling depths Redistribution of upwelled water along the coast .
Offshore transport Poleward of transport upwelled of tracer tracer released in the subsurface
Tracer release 150- 250 m
Combes et al 2013 Nutrient budget for one region
At the Santa Barbara Channel Site, for example, it was determined that nitrate supply was mediated by
1. Coastal upwelling (70%) 2. Summer internal waves (9-12%) 3. Winter upwelling (7-12%) 4. Terrestrial runoff (2-15%)
Vertical mixing is critical for the nutrient budget of the surface ocean (and processes that act to change the extent of this mixing can have serious consequences for ecosystem productivity)
McPhee-Shaw et al. 2008 Concepts Introduced in the Martz Paper
Upwelling redistributes elements essential for biological production
Gas exchange alters upwelling “signature”
Why the focus on nitrate?
Redfield ratio f-ratio
What do ratios of upwelling nutrients tell us about all of the above? Concepts Introduced in the Martz Paper
Upwelling redistributes elements essential for biological production
Gas exchange alters upwelling “signature”
Why the focus on nitrate?
Redfield ratio f-ratio
What do ratios of upwelling nutrients tell us about all of the above? Uptake of nitrate in the inshore region is positively correlated with rates of primary production (2011 CCE LTER Cruise)
80.00 1 - 70.00 day 1 - 60.00
g C L 50.00 µ
40.00
30.00
20.00
10.00 Primary Production 0.00 0 0.05 0.1 0.15 Nitrate uptake (into phytoplankton) µM N L-1 day-1 M. Stukel, unpublished Practical reason: There is a nitrate sensor, But nitrate is a good tracer of CCE productivity Nitracline can be used as a measure of the variability of nitrate supply into the euphotic zone, and thus potential euphotic zone productivity
Mantyla et al., 2008 Long term indices of primary production are correlated with the concentration of nitrate at the nitracline depth Values represent seasonally-corrected anomalies and smoothed using a 6-month running average over 2004-2016
In situ measured chlorophyll concentration at the depth where chlorophyll reaches its peak
Satellite based calculation of net primary production (NPP) ~nitracline depth ~nitracline
(Net primary production (NPP) = gross primary production – phytoplankton respiration) Concepts Introduced in the Martz Paper
Upwelling redistributes elements essential for biological production
Gas exchange alters upwelling “signature”
Why the focus on nitrate?
Redfield ratio f-ratio
What do ratios of upwelling nutrients tell us about all of the above? The Redfield Average in seawater
Ratio. Eastern Pacific in particular, has a little bit less nitrate relative to the Redfield Ratio
In vast areas of the Pacific, N is a limiting nutrient
REDFIELD RATIO (average in phytoplankton):
(CH2O)106(NH3)16(H3PO4) + 138O2 ó106CO2+ 16HNO3 + H3PO4 + 122H2O Phytoplankton average composition Biology requires a variety of elements for growth
- - C: as CO2, HCO3 , CO3 (sometimes referred to as DIC)
- - + N: NO3 (NO2 ), NH4 , in rare cases N2.
2- P: HPO4 (or 3- abbreviated as PO4 )
Si: H2SiO3 (might see 100 fold excess relative to N other versions of this, e.g., Si, SiO2) 10 fold excess relative to N
Fe limitation has 100 fold deficient relative to N been shown to be very relevant for the CCE
Moore et al., 2013 Concepts Introduced in the Martz Paper
Upwelling redistributes elements essential for biological production
Gas exchange alters upwelling “signature”
Redfield ratio
Why the focus on nitrate? f-ratio
What do ratios of upwelling nutrients tell us about all of the above? f-ratio: New nitrogen versus recycled nitrogen and new production
In its simplest form new production refers to the N2 primary production facilitated by sources of N external to the euphotic zone. In our system new N is primarily supplied by upwelling.
Euphotic Zone Phytoplankton
NH4 +
Below the Euphotic
Zone - - NH4 NO2 NO3 +
In contrast, total production includes phytoplankton production fuelled by ammonium (recycled) f-ratio definition
New production
(The amount of production fueled by new sources of nitrogen) f-ratio = (The amount of production fueled by all source of N (i.e., new and recycled))
If you were measuring NO3:CO2 ratios in seawater, how would recycled N driven production manifest in your data? Concepts Introduced in the Martz Paper
Upwelling redistributes elements essential for biological production
Gas exchange alters upwelling “signature”
Redfield ratio
Why the focus on nitrate? f-ratio
What do ratios of upwelling nutrients tell us about all of the above? The anatomy of CCE2 http://mooring.ucsd.edu/projects/cce/img/cce2_08_design.png http://mooring.ucsd.edu/dev/cce2/cce2_11/ In the CCE, ratios are remarkably well conserved in a general sense. Therefore changes in concentration are due to production, respiration, and mixing.
Did they measure DIC directly? - NO3 : X affected by uptake of non-nitrate N O2 equilibrates faster than CO2 - When NO3 approaches 0 continued production of O2 and consumption of CO2 must be linked to regenerated N production “The resulting time series contains variability due to daily production and respiration and mixing associated with processes such as diel changes in mixed layer depth. The effects of lower frequency processes such as upwelling and relaxation are largely removed by the high-pass filter. As described by Johnson [2010], the filtered time series contains information on the local stoichiometric relationship between carbon, oxygen, and nitrogen. Uptake/remineralization ratios were calculated using a Type II regression for the filtered time series as a whole and piecewise using a shifting 5 day window to examine temporal variability.” Let’s look at the 5-day data from the automated sensors - that measure nitrate (NO3 ), oxygen (O2) and dissolved ? ? inorganic carbon (DIC) in surface waters
0 nitrate
This ratio is unaffected by gas exchange
Despite decrease in upwelling events there is no clear transition from new to regenerated production dominated time periods. But (blue box)…. 0 nitrate “Divergence of the sensor data from the Redfield ratio is possible through several different processes. As mentioned above, significant regional differences in particle C:P and C:N ratios have been observed and attributed to differences in phytoplankton lineage [Martiny et al., 2013]. Deviations in DIC:O2 may result from gas exchange, as O2 equilibrates with the atmosphere more rapidly than CO2. This leads to reduced amplitude in the filtered oxygen data, forcing the slope in Figure 1b to a more negative value than the Redfield ratio. Both the NO3:DIC and NO3:O2 ratios (Figures 1a and 1c) are affected by the - source of nitrogen taken up by phytoplankton. NO3 :O2 is also affected by O2 gas exchange. However, the close agreement between Redfield values and both ratios involving NO3(Table 1) suggests little (<10%) Regenerated Production at CCE-2. In other words, the f ratio [Eppley and Peterson, 1979] computed by combining the sensor data with Redfield ratios is close to 1. It is noteworthy that Johnson [2010] observed very different ratios in Monterey Bay, CA, using similar sensors and data processing. For comparison, these numbers are included in Table 1.” The anatomy of CCE2
15m sensor package CCE 2 measurements are made Temperature: Seawater temperature at 15 m depth varies because of changes in heat flux between the atmosphere and between 15-17 m below surface ocean ocean, variations in ocean currents, vertical mixing, and internal waves. Salinity: Salinity at 15 m depth varies because of changes in evaporation and precipitation, variations in ocean currents, vertical mixing, and internal waves. Density: Seawater density (sigma) depends primarily on the water's temperature and salinity. The density of surface seawater deviates only up to 3 percent from 1000 kg/m³. The oceanographer simplifies the density to sigma, the deviation from 1000 kg/m³: sigma = density[kg/m³] - 1000 kg/m³ Nitrate Sensor: Our SUNA nitrate sensor measures dissolved inorganic nitrogen (mainly nitrate and nitrite) in seawater. Nitrate is an important nutrient source for phytoplankton growth pH and O2 at 15 m also.
DIC and O2 sensors at surface