Nutrients; Aerobic Carbon Production and Consumption

Transcription

1 Nutrients; Aerobic Carbon Production and Consumption OCN 623 Chemical Oceanography 5 February 2013 Reading: Libes, Chapters 8-10

2 Outline 1. Overview - photosynthesis & respiration 2. Nutrients - chemical info 3. Nutrient regeneration - effect on vertical nutrient profiles 4. Nutrient trends across the oceans 5. Apparent oxygen utilization (AOU) in the ocean 6. Composition of particles driving AOU

3 Redfield-Richards Equation The next few lectures can be summarized by the Redfield-Richards Equation: P CO 2 + N + P + H 2 0 Organic matter + O 2 We will look first at the so-called inorganic nutrients : R N, P and Si They are also called biolimiting elements -- Why? 1. Small reservoir size in oceans 2. Fast turnover time 3. Required for many kinds of biological activity

4 Inorganic Nutrients 1. Physical Speciation (operational definitions!) A. Dissolved -- pass thru a specified filter (e.g., 0.45 µm pore size) B. Particulate -- retained by a specified filter C. Colloidal -- pass thru conventional filters, but are not dissolved

5 2. Chemical Speciation A. Phosphorus i. Dissolved Inorganic Phosphorus (DIP) a. ph-dependent speciation of Orthophosphate: H 3 PO 4 H 2 PO - 4 HPO 4 2- (most important at sw ph) PO 4 3- b. Polyphosphate linked phosphate polymers ii. Dissolved Organic Phosphorus (DOP) e.g., Phospholipids, ATP, ADP

6 B. Nitrogen Redox-dependent speciation of dissolved forms: Dissolved Inorganic Nitrogen (DIN) Dissolved Organic Nitrogen (DON) Species Oxid State NO - 3 (nitrate) +V NO - 2 (nitrite) +III N 2 O (nitrous oxide) +I N 2 (dinitrogen) 0 NH 4+ or NH 3 -III Nitrate + nitrite Organic-N -III (e.g., Urea H 2 N-CO-NH 2 ) NH 4+ (ammonium ion) NH 3 (ammonia )

7 C. Silica Soluble forms: H 2 SiO 3 (95% of total dissolved silica over a broad ph range) HSiO - 3 (5% of total dissolved silica) SiO 2-3 (<<1% of total dissolved sillica)

8 Nutrient Regeneration and AOU (dissolved species)

9 RESPIRATION Modified from Sarmiento & Gruber 2006

10 Nutrient Vertical Profiles ( µm ) ( µm ) ( µm )

11 Open-Ocean Nutrient Profiles Phosphorus Main processes controlling vertical distribution of nutrients: [P] several µmol L -1 High consumption of inorganic nutrients; high production of organic nutrients Depth Slow release of inorganic nutrients due to decomposition of falling particles; slow utilization of organic nutrients 2000 m DOP DIP

12 Open-Ocean Nutrient Profiles - Nitrogen [N] tens of µmol L -1 Depth NH 4 + NO 2 - Low-[O 2 ] loss of NO 3 - (denitrification) 2000 m DON NO - O 2 3 Denitrification (nitrate reduction): 2NO 3- + CH 2 O + 8H + + 6e - N 2 + CO 2 + 5H 2 O

13 Nitrite - An Indicator of Suboxia Typically, nitrate and nitrite are measured together (reported as their sum). However, nitrite maxima can be observed: Subsurface maximum (presumably due to suboxic zone in/on particles O 2 -minimum zone maximum NH 4+ profiles look similar (two maxima)

14 Oxygen Nutrient Diagrams Redfield-Richards Equation in Action NW Pacific Slope -120 µm O 2 µm PO 4 Slope -12 µm O 2 µm NO 3 Redfield: AOU/ P = 138/1 = 138 AOU/ N = 138/16 = 9 Actually, NO 3- + NO 2-. For simplicity, ignore NH 4 +

15 Why Are Nutrient Concs Different in Each Ocean? Look at Ocean Net Flow at 4000 m

16 Figure 10.3a Dissolved Oxygen at 4000 m

17 Figure 10.3d Dissolved Nitrate at 4000 m

18 Measurement & Use of AOU Equator [Preformed] N [Measured] For biogeochemically regenerated elements in seawater, the Redfield- Richards Equation indicates: [Measured] = [Preformed] + [Oxidative] [Oxidative] Change in conc due to organic matter oxidation

19 [Measured] = [Preformed] + [Oxidative] [P] [O 2 ] Depth Depth AOU - [O 2, oxidative ] AOU P preformed P oxid P measured O 2, measured O 2,preformed

20 Apparent Oxygen Utilization at 4000 m From Libes (2009) website

21 (mol/l) (Solve for C)

22 Use appropriate local Redfield (C:P) ratio

23 AOU and Denitrification Figure 10.6 Denitrification (nitrate reduction): 2NO 3- + CH 2 O + 8H + + 6e - N 2 + CO 2 + 5H 2 O

24 Particle Composition Spatial differences Temporal differences (highest C:N due to lack of nutrients) C : N

25 Homework Due: Tues, 12 Feb Using online HOT data ( for Station ALOHA, calculate the C:N:P ratio of sinking particulate organic matter in the top 800 m of the North Pacific Gyre in March Are the ratios you calculate reasonable? 2. Compute the AOU of the 4000-m deep water at Station ALOHA. How do your results compare with the results shown in class? For both questions: Be sure to show all of your calculations, and explain exactly what data you used.