Optics of Marine Particles

Transcription

1 Optics of Marine Particles Lecture 2 Dariusz Stramski Scripps Institution of Oceanography University of California San Diego dstramski@ucsd.edu IOCCG Summer Lecture Series 22 July - 2 August 2014, Villefranche-sur-Mer, France

2 Suspended Particulate Matter Plankton microorganisms Biogenic detrital particles Mineral particles Colloidal particles Air bubbles

3 Plankton microorganisms

4 Plankton microorganisms (Stramski et al., 2001)

5 Interspecies variability in absorption (Stramski et al. 2001)

6 Interspecies variability in scattering (Stramski et al. 2001)

7 1.0 Interspecies variability in single scattering albedo Single scattering albedo Light wavelength [ nm ] (based on data from Stramski et al. 2001)

8 Mie calculations of scattering phase function for plankton microorganisms (Stramski et al. 2001)

9 Backscattering properties of plankton microorganisms (subject to uncertainties associated with Mie scattering calculations for homogeneous spheres) (Stramski et al. 2001)

10 Intraspecies variability due to irradiance - Synechocystis Absorption Scattering Cell Chl C WAVELENGTH [ nm ] (Stramski and Morel 1990)

11 Intraspecies variability due to temperature, nitrogen, and light limitation Thalassiosira pseudonana Absorption vs. growth rate Scattering vs. growth rate (Stramski et al. 2002)

12 Intraspecies variability over a diel cycle Thalassiosira pseudonana (Stramski and Reynolds 1993)

13 Optical variability for heterotrophic bacteria Absorption Beam attenuation CHB Carotenoid-rich bacteria: grown in nutrient-enriched seawater [EX-1 (light-dark cycle), EX-2 and EX-3 (dark)], and in nutrient-poor seawater (EX-4) NHB Non-pigmented bacteria: fast-growing in the absorption experiment and starved in the attenuation experiment (Stramski and Kiefer 1998)

14 Prey-predator interactions (cyanobacteria and ciliates) Particle size distributions Absorption spectra Scattering spectra (Stramski et al. 1992)

15 Examples of particulate absorption coefficients a p, a d or NAP, a ph (data from the Sargasso Sea) a ph = a p - a d or NAP (Bricaud and Stramski 1990)

16 Example non-algal particle (NAP) absorption spectra and the corresponding exponential fits for different regions (Babin et al. 2003)

17 Frequency distribution of spectral slope of NAP absorption NAP absorption spectra calculated with a NAP (443)=1 m -1 and S NAP = nm -1 (±1.96 standard deviation, where SD= nm -1 ) (Babin et al. 2003)

18 Mineral particles Spitsbergen fjord, Arctic Saharan dust Mongolian Cyclone 7 April 2001 Cloud Dust

19 Sample ID Description Origin ILL 1 illite Source Clay Minerals Repository, University of Missouri (ref. IMt-1) Terrigenous mineral-rich particulate matter (Stramski et al. 2007) ILL 2 as above but different PSD as above KAO 1 kaolinite (poorly crystallized) as above (ref. KGa-2) KAO 2 as above but different PSD as above MON 1 Ca-montmorillonite as above (ref. SAz-1) MON 2 as above but different PSD as above CAL 1 calcite natural crystal CAL 2 as above but different PSD as above QUA 1 quartz natural crystal SAH 1 atmospheric dust from Sahara red rain event, Villefranche-sur-Mer, France SAH 2 as above but different PSD as above AUS 1 surface soil dust cliff shore, Palm Beach near Sydney, Australia AUS 2 as above but different PSD as above ICE 1 ice-rafted particles glacier runoff, Kongsfjord, Spitsbergen ICE 2 as above but different PSD as above OAH 1 surface soil dust Oahu, Hawaii Islands OAH 2 as above but different PSD as above KUW 1 surface soil dust Kuwait (eastern part, close to ocean) KUW 2 as above but different PSD as above NIG 1 surface soil dust southwest Nigeria SAN 1 atmospheric dust San Diego, California

20 Mass-specific absorption Mass-specific absorption coefficient a p * (m 2 g -1 ) SAH OAH 2 b KUW OAH NIG KUW SAN AUS 1 ILL 2 KAO 2 AUS 2 MON 2 ICE 2 SAH 2 QUA 1 CAL 1 ICE Light wavelength (nm) a c Mass-specific scattering Mass-specific scattering coefficient b p * (m 2 g -1 ) 2.0 ICE 1 ICE 2 SAH AUS SAH 1 AUS SAN 1 KUW 1 KUW OAH 2 OAH 1 NIG ILL 2 KAO 2 MON 2 CAL CAL 1 c ILL MON 1 KAO 1 QUA 1 MON Light wavelength (nm) a b (Stramski et al. 2007)

21 Particle Size Distributions Particle number concentration FN(D) (m -3 m-1) SAH 1 SAH 2 a a 1 10 KUW 1 KUW 2 b Particle volume concentration FV(D) ( m -1 ) 6x10-6 5x10-6 SAH 2 4x10-6 SAH 1 3x10-6 2x10-6 1x10-6 SAH x10-6 5x10-6 KUW 2 d 4x10-6 3x10-6 2x10-6 KUW 1 1x10-6 KUW 2 c Particle equivalent diameter D ( m) Particle equivalent diameter D ( m) (Stramski et al. 2007)

22 Absorption of mineral-rich particulate assemblages Mass-specific absorption Fe-specific absorption (Babin and Stramski 2004)

23 (Babin and Stramski 2004)

24 Asian dust - sampling locations (Stramski et al. 2004)

25 Asian mineral-rich dust (Stramski et al. 2004)

26 Colloidal particles (< 1 m in size) undergoing Brownian motion

27 Size distributions of colloids Particle concentration N(D)dD ( m -3 ) Scotian shelf 5 m Scotian shelf 10 m Scotian slope 20 m Scotian slope 40 m Sargasso Sea 30 m Sargasso Sea 50 m Sargasso Sea 70 m Southern Ocean shelf 40 m S. Ocean open waters 3 m S. Ocean open waters 30 m S. Ocean open waters 50 m Wells and Goldberg (1994) Particle diameter D ( m ) Particle concentration N(D)dD ( m -3 ) Station B 0 m Station B 33 m Station C 0 m Station C 23 m Station D 0 m Station D 34 m Station D 55 m Yamasaki et al. (1998) Particle diameter D ( m ) Otsuchi Bay 5 m Otsuchi Bay 25 m Otsuchi Bay 40 m

28 Scattering coefficient b ( m -1 ) Wavelength ( nm ) Backscattering coefficient b b ( m -1 ) 10-2 Results for colloidal particles scattering Wavelength ( nm ) Backscattering coefficient b b ( m -1 ) backscattering Wavelength ( nm ) Wavelength ( nm ) pure seawater pure seawater average small colloids average average small large colloids small + large colloids average large small + large colloids (Stramski and Woźniak 2005)

29 Light scattering by bubbles entrained by wave breaking (Stramski and Tęgowski 2001)

30 Scattering and backscattering by bubbles as a function of void fraction (Terrill et al. 2001)

31 Traditional approach Inherent Optical Properties (IOPs) described in terms of a few broadly-defined categories of seawater constituents IOP( ) = IOP w ( ) + IOP p ( ) + IOP CDOM ( ) IOP p ( ) = IOP ph ( ) + IOP NAP ( ) Example IOPs: absorption coefficient, scattering coefficient, beam attenuation coefficient, volume scattering function

32 A four-component model of absorption

33 Chlorophyll-based approach IOP( ) = IOP w ( ) + f [ Chla ] for example a ph ( ) = f [ Chla ] a p ( ) = f [ Chla ] AOP( ) (e.g., ocean reflectance) = f [ Chla ]

34 Case 1 and Case 2 Waters Morel and Prieur (1977); Gordon and Morel (1983)

35 Absorption vs. chlorophyll-a ~ 4-fold variation (Bricaud et al. 1998)

36 Beam attenuation vs. chlorophyll > 10-fold variation (Loisel and Morel 1998)

37 Chlorophyll Algorithm OC4 Algorithm (Clarke, Ewing & Lorenzen 1970) (O Reilly et al. 2000)

38 Global distribution of phytoplankton chlorophyll in the world s oceans from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) based on Sep Feb 2007 data Courtesy of NASA

39 Chlorophyll-based approach: Summary Parameterization in terms of chlorophyll-a concentration alone Empirical regressions (statistically-derived models) Provide average trends but no information about variability Not valid for Case 2 waters Not necessarily satisfactory for Case 1 waters

40 Reductionist approach To develop an understanding and assemble a model of the whole, from the reductionist study of its parts IOP p ( ) IOP ( ) k, pla k IOP ( ) m m,min IOP ( ) n n,det plankton minerals detritus

41 Example criteria Manageable number of components The sum of components should account for the total bulk particulate and optical properties as accurately as possible The components should play specific well-defined roles in ocean optics and biogeochemistry

42 Example reductionist model of particle functional types (PFTs) Living Particles Autotrophs 1. Picophytoplankton <2-3 m (prokaryotes and eukaryotes) 2. Small nanophytoplankton ~2-8 m 3. Coccolithophores 4. Large nanophytoplankton ~8-20 m 5. Microphytoplankton m Heterotrophs 6. Bacteria ~0.5 m 7. Microzooplankton O(1-100) m Non-Living Particles Organic 8. Small colloids m 9. Coarse colloids m 10. Detritus >1 m Inorganic 11. Colloidal/Clay minerals <2 m 12. Larger (Silt and Sandsized) minerals >2 m Challenge: Characterization of PFT properties e.g., optical cross-sections concentration in seawater s ( ) i N i

43 Multi-component model of bulk IOPs IOP( ) j i 1 IOP ( ) N i j i 1 i s i ( ) N i

44 Example IOP model with detailed description of plankton community (Stramski et al. 2001)

45 Size distribution (Stramski et al. 2001)

46 Absorption Scattering (Stramski et al. 2001)

47 Reductionist IOP/radiative transfer/reflectance model Input to radiative transfer model IOP( ) j i 1 IOP i ( ) N j i 1 i s ( ) i Output, e.g. ocean reflectance j i 1 R( f [ Ni s i, a( ), Nis i, b(, )] j i 1 In what ways does variability in detailed seawater composition determine variability in ocean reflectance? What information about water constituents and optical properties can we hope to extract from remotely sensed reflectance?

48 Multi-component IOP database Radiative transfer model (Stramski and Mobley 1997; Mobley and Stramski 1997)

49 Reductionist approach: What do we need to do? Optical measurements include b(, ); target specific water constituents Particle identification and characterization particle species composition, size distribution, particle chemistry, biology, mineralogy, etc. Laboratory experiments (not just field experiments) New techniques and instrumentation

50 The complexity of seawater as an optical medium should not deter us from pursuing the proper course in future research The reductionist worldview has to be accepted as it is, not because we like it, but because that is the way the world works Steven Weinberg 1979 Nobel Prize in Physics