Macronutrients in the ocean

Transcription

1 Macronutrients in the ocean Philip Boyd NIWA/OTAGO, New Zealand September 2011 OUTLINE What is a macronutrient? Trends in nutrients & limitation The N cycle sources, sinks and recycling Silicate the body builder Stoichiometry - The N and P cycles Climate change & macronutrients

2 What is a macronutrient? An element, such as carbon, hydrogen, oxygen, or nitrogen, required in large proportion for the normal growth and development of a plant What are they required for? The synthesis of macromolecules such as lipids, proteins and carbohydrates NOAA 1994, Levitus Joseph Wright

3 THE ELEMENTS OF MICROBIAL LIFE Component Composition Nucleus (DNA) C-N-P Ribosome (RNA) C-N-P Membranes C-P Cell wall Proteins/enzyme s/ flagellum Storage bodies: PHB Poly-P C-N C-N C P The elements required for each macromolecular group are defined by the structure of the molecule, e.g. nucleotides comprise a phosphate group, a carbohydrate molecule and a N-containing base

4 Many complex pathways after nutrient uptake Capone 1992

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6 Uptake rate (V) Nutrient uptake kinetics V max1 V max2 ½ V max1 Active uptake by membrane transporters ½ V max2 Internal storage pool K s1 K s2 Substrate concentration (S)

7 Global nutrient distributions - Phosphate

8 Global Nutrient distributions

9 Nutrient limitation patterns - Diatoms (Moore et al., 2004).

10 Nutrient limitation patterns N fixers

11 The Biogeochemical cycle of N in the ocean Lipschultz et al. (2000)

12 N 2 FIXATION Discovered in late 19 th century in soil bacteria H. B. Bigelow (1931): The possibility that so-called N 2 fixers may also fertilize seawater must be taken into account Dugdale discovered N 2 fixation in Sargasso Sea in 1961 Process was considered to be negligible in the 1980 s, but significant since JGOFS

13 Boyd & Hurd (2009)

14 N 2 FIXATION AT STATION ALOHA ( ) N 2 accounts for 47±9% of new N Large interannual variations: 36% in 1993 vs. 69% in 1999 Relative importance of N 2 vs. NO 3 - as a source of new N has increased since 1995 Karl et al. (2002)

15 Sinks for N Seasonal trends in nutrient profiles NO3 (µmol L -1 ) Depth (m) winter 2004 spring 2005 summer 2005 autumn Boyd & Hurd (2009) Boyd & Hurd Figure 6

16 N preferences at HOT - SPSG Prochlorococcus prefers NH 4+ /DON but some phylotypes can use NO 2 - Eukaryotic phototrophs use NO 3 - and possibly DON, and compete with all others for NH 4 + Heterotrophic bacteria may prefer NH 4+ /DON but can also use NO 3 - /NO 2 - Diazotrophs use N 2

17 THE FOODWEB AND NITROGEN CYCLING f ratio = (new N/(new N + regenerated N))

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19 An N Cycle summary - an annual budget Karl et al. (2002)

20 The biological pump recycles macronutrients gt C yr -1 It is in balance over long timescales (years) as: PON export 7-16 gt C yr -1 NO 3 Eppley & Peterson (1979)

21 Nutrient remineralization length scales Export N depth Role of bacteria C Si Fe

22 nitrification Classic von Brand & Rakestraw diatom rotting experiment of 1935!

23 A typical nutrient profile

24 Why such a difference in These nutrient profiles?

25 Regional differences due to age of the water mass Determines potential productivity of the basin

26 Arrigo (2005)

27 Courtesy Mary Silver (UCSB) Silicate the body builder

28 Architecture and material properties of diatom shells provide effective mechanical protection Frustules are remarkably strong by virtue of their architecture and the material properties of the diatom silica Hamm et al. (Nature 421, ) The evolutionary arms race between diatoms and their specialized predators will have had considerable influence in structuring pelagic food webs and biogeochemical cycles

29 Broken diatom frustules are indicators of mortality Fragilariopsis kerguelensis Discoid diatoms Courtesy V. Smetacek (AWI)

30 Fe supply impacts the uptake stoichiometry of silicate relative to nitrate And SILICIFICATION 1.0 nitrate depletion silicic acid depletion 0.8 mmol m -3 d Fe -Fe Days Boyd et al. (2005) Under low Fe diatoms produce thicker frustules

31 Biogenic silica / opal - mineral ballast particle sinking Radiolarian Diatom Phaeodarian

32 Global distribution of silicate V. Smetacek (AWI) NOAA 1994 Levitus

33 Insights into diatom blooms in the geological past are obtained from sediment cores Marked increases in productivity & rapid settling of biogenic matter are suggested in cores by the episodic accumulation of diatomaceous oozes up to 1 m thick!

34 Rivers 5.0 Ocean biogeochemical cycle of Silica (Trequer et al. 1995) Biol. Uptake And recycling Mixed layer Eolian 0.5 Upwelled Hydrothermal basalt Teramoles of Si /year

35 Nutrient Stoichiometry - The N and P cycles Stoichiometry refers to patterns of mass balance in chemical conversions of different types of matter, which often have definite compositions. Sterner and Elser (2002)

36 Further definitions Sterner & Elser (2002) Ecological stoichiometry--the balance of multiple chemical substances in ecological interactions and processes. Elemental imbalance--dissimilarity in nutrient content between two things, such as between an autotroph and the inorganic medium. If a consumer and resource have identical stoichiometry, they are perfectly balanced. The greater they differ, the more their imbalance.

37 REDFIELD STOICHIOMETRY OF LIFE C 106 :N 16 :P 1 Carbon Nitrogen Phosphorus C:N = 6.6 / C:P = 106 / N:P = 16

38 REDFIELD STOICHIOMETRY OF LIFE C 106 :N 16 :P 1 Carbon Nitrogen Phosphorus Initially thought to be the imprint of the synthesis of macromolecules including lipids, proteins and carbohydrates

39 Atlantic Ocean N:P = 20 Redfield (1934) THE RATIO Redfield (1934) N:P = 20 Cooper (1937/1938) N:P ratio redefinition based on salt correction of 1.35x for P analyses! Today N:P = Courtesy D Karl

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41 R. Geider and J. La Roche (2002) Redfield revisited: variability of C:N:P in marine microalgae and its biochemical basis Eur. J. Phycol. 37: 1-17 C:N:P is plastic, not fixed N P limitation transition much higher than 16:1 General conclusion: Our analysis suggests caution in application of the Redfield Ratio in theoretical biogeochemical analyses and as a conversion factor in field studies.

42 Klausmeier et al. (2004)

43 Their results show that the canonical Redfield N:P ratio of 16 is not a universal biochemical optimum, but instead represents an average of species-specific N:P ratios. Klausmeier et al. (2004)

44 N:P ratios and physiological strategies Arrigo (2005)

45 Experimental Variation of the C:N:P Ratios (by Atoms) in Cultures of the Freshwater Alga, Chlorella pyrenoidosa (Ketchum and Redfield, 1949) Conditions C N P Normal cells Phosphorus deficient cells Nitrogen deficient cells Elemental imbalance--dissimilarity in nutrient content between an autotroph and the inorganic medium.

46 N:P differences are evident within the biogeochemical cycles Arrigo (2005)

47 Using the Redfield ratio perspective i.e. P* Basin-scale differences North Atlantic P* < 0, P limited South Atlantic P* > 0, N limited Moore et al. 2008

48 Are changes in P* due to N fixation or N:P uptake of other phytoplankton?

49 CASE STUDY STA. ALOHA EZ SRP has decreased by >80% over past 17 years How low can it go?

50 Climate change and macronutrients Boyd and Doney (2002) Doney (2006)

51 Figure 2a. Total NOy+NHx Deposition in 1860, mg N m-2 yr-1

52 Figure 2c. Total NOy+NHx Deposition in 2050, mg N m-2 yr-1

53 Anthropogenic AN provides around 32% of external N supply Duce et al. 2008

54 S u c h More N fixers Due to warming? Boyd & Doney (2002)

55 Coccolith Other environmental controls on A) N fixers? 0 High CO 2 Greenhouse Ambient High Temperature Calcite (g C ( B High CO 2 Greenhouse Ambient High Temperature 4 4 N 2 fixation rate (nmol N mol C -1 h -1 ) Pa 39 Pa 76 Pa C) N 2 fixation rate (nmol N mol C -1 h -1 ) Pa 39 Pa 76 Pa D pco 2 pco 2 Hutchins et al. (2007) Moisander et al. (2010)

56 What is needed Surveys e.g. AMT

57 And new modelling approaches Follows (2007)

58 Conclusions Macronutrients play a key role in setting the productivity of the oceans Their biogeochemical cycles are tightly interlinked via stoichiometry yet they are also flexible Other factors such as trace element supply and climate-mediated changes can subtly alter these links Climate change will impact the biogeochemistry of macronutrients in a complex manner