Geochemical proxies in Marine and Lake Studies

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1 Geochemical proxies in Marine and Lake Studies Stable isotopes: oxygen and carbon Inorganic Geochemistry: elemental distributions Organic Geochemistry: Organic ve inorganic carbon Clay mineral distributions Microfossil assemblages (e.g., forams and ostracods)

2 Paleoceanography and paleolimnology reconstruction of past environmental conditions and processes Processes: Physical (water circulation, water mass formation, water mass stratification, sediment transport and deposition) Biogeochemical (nutrient cycling, organic matter production and carbon export, bottom water oxygen conditions, nutirents) Geological (tectonics, uplift, opening and closing of gateways) The sedimentary records of these processes are found in sedimentary successions as: Microfossil populations, Organic matter Elemental and isotopic composition of fossil shells Mineralogical Main objective and of these chemical studies composition is the reconsctruction of detrital sedimentary of the matter past climates and environments.

3 Proxy Proxy is a measurable parameter that stands in for a paleo-environmental target variable such as temperature and salinity. T = f (P) Examples: Target parameter (T) => Proxy (P) Sea surface temperature => Alkenone ratio Salinity and temperature => oxygen isotopes Organic productivity => Organic-C, Ba, C-isotopes Nutrients => Cd/Ca Bottom water oxygen conditions => Benthic foraminifers and Mn Mean sea surface temperature => Pelagic foraminifer species distribution These proxy parameters are calibrated and transferred to target parameters using transfer equations based on exprerimentally determined or present day measurements.

4 Target parameter Proxy Temperature(SST) Salinity Organic productivity Bottom water oxygen conditions Age of deep water masses Nutrients Vegetation and climate changes Microfossil assemblage(foraminifer) δ 18 O calcite Mg/Ca, Sr/Ca U K 37 alkenons Microfossil assemblage δ 18 O calcite TOC, Carbonate Opal, barite, δ 13 C Bentic foraminifer and ostracoda, Mn δ 13 C Cd/Ca Pollen δ 13 C (C3 and C4 type plants)

5 Stable Isotopes Hydrogen : 1 H, 2 H (Deuterium), 3 H (Tritium) Carbon : 12 C, 13 C, 14 C (radioactive) Oxygen : 16 O, 18 O, 17 O (very low abundance) Sulphur : 32 S, 34 S, 37 S & 36 S (very low abundance) Nitrogen) : 14 N, 15 N

6 BASIC PRINCIPLES FOR STABLE ISOTOPES There is a large relative mass difference between isotopes of the elements of low atomic number. As a result such light isotopes behave differently and fractionate in physical, chemical and biological processes to a greater degree than do isotopes of heavy elements. Isotopic fractionation between light and heavy isotopes is the result of differences in the vibrational frequency of the isotopes in a molecule or crystal structure. Heavy isotope has a low vibrational frequency and forms stronger bonds with atoms of other elements than does the light isotope. This difference in the bond strength is relatively much larger for isotopes of light elements than it is for isotopes of the heavy elements.

7 ISOTOPIC FRACTIONATION Isotopes of an element behave differently, and thus fractionate in physical, chemical and biological reactions. Fractionation occurs in two forms: Chemical equilibrium fractionation (isotopic exchange) Kinetic fractionation (different reaction rates for different isotopes) Isotopic fractionation during chemical equilibrium occurs as isotopic exchange, and does not result in a large isotopic fractionation between the isotopes of a given element. Kinetic fractionation creates a greater isotopic fractionation than the chemical fractionation.

8 PHYSICAL FRACTIONATION Evaporation is a good example: This results in enrichment of light isotopes in the vapour phase and heavy isotope in the remainng liquid phase. CHEMICAL FRACTIONATION Isotope exchange takes place in the form of chemical equilibrium. For example in solution of carbondioxide in water: ½ C 16 O 2 + H 2 18 O ½ C 18 O 2 + H 2 16 O In this equation the isotope exchange takes place until the four different compounds isotopically reach equilibrium. In case of equilibrium, the isotopic ratio ( 18 O/ 16 O) in CO 2 ve H 2 O will not be the same because the bond strengths of the different oxygen isotopes in CO 2 ve H 2 O are different.

9 KINETIC FRACTIONATION The isotope with a lighter mass has a faster reaction rate than the isotope with a heavier mass. This difference in behaviour is especially important in biochemical reactions. In biogeochemical reduction reactions, organisms can break the compounds of the lighter isotopes much faster than they break the compounds of the heavy isotopes. In this way they greatly cause enrichment of the lighter isotopes in the reduced reaction products. In a closed sytem, the oxidized reaction products would be enriched in the heavy isotopes. The best examples of biogeochemical (kinetic) fractionation are observed for C and S isotopes.

10 UNITS USED IN STABLE ISOTOPE ANALYSES Isotope analyses are carried out using mass spectrometers (MS). Stable isotope ratios rather than individual absolute isotope amounts are measured in MS analysis. The results are expressed as ratios of heavy/light isotope (e.g., 18 O/ 16 O), with respect to a standard in value having per mil or unit: = {(R sample /R standard ) -1}x1000 Where R is the ratio of the heavy/light isotope in sample (R sample ) or in the Standard (R standard ).

11 Standards used in stable isotope analysis Isotope Hydrogen ( 2 H/ 1 H) Oxygen ( 18 O/ 16 O) Carbon ( 13 C/ 12 C) Sulphur ( 34 S/ 32 S) Standard Standard Mean Ocean Water (SMOW) For water analysis: SMOW; for carbonate analysis: PDB (Pedee Formation belemnite - calcite) PDB CDT (Canyon Diablo meteorite - triolite)

12 Oxygen Isotopes Seawater oxygen isotope value is a function of three important parameters: 1) Ice volume: as the ice volume in polar regions increases, the seawater 18 O value increases 2) Salinity (which is a fuction of precipitation/evaporation ratio): Precipitation/ Evaporation ratio decrease the 18 O value of seawater 3) Temperature: Lighter isotope tends to concentrate in compounds (e.g., calcite) with increasing temperature ( 18 O is lowered with increasing temperature)

13 Temperature effect The difference between the vibration frequencies of two isotopes increases with increasing temperature according to the following relationship: log 18 O = A 1/T 2 + B Where A and B are constant for the studied specific system, and can be measured experimentally. Using this relationship paleo-ts can be measured. According to this relationship, 18 O value decrease with increasing T, and 16 O isotope enters the crystal structure (e.g,calcite) more easily than does 18 O.

14 OXYGEN ISOTOPES AND TEMPERATURE RELATIONS There is an emperical relationship between the oxygen isotopic composition of the organically or inorganically precipitated carbonate (δ 18 Oc) and the temperature (T C) and isotopic composition (δ 18 Ow) of the water from which the preciptation takes place (Epstein et al., 1953): T = (δ 18 O c -δ 18 O w ) (δ 18 O c - δ 18 O w ) 2

15 There is a reciprocal relationship between temperature and δ 18 Oc Every unit corresponds to a temperature difference of 5 C Glacial-Interglacial pelagic foraminifer δ 18 O c values differ by 1.2 (Sackleton and Opdyke, 1973; Berger et al., 1993). This corresponds to a difference of about 5.5 C (cumulative of T and ice volume effects) Fresh water effect on the oxygen isotope values is lower in the tropical regions than in the middle and higher latitudes (Fairbanks, 1992).

16 According to the Epstein equation, there is a direct relationship between the seawater δ 18 Ow value and seawater salinity (S, ). For example this reltionship for the presentday Sea of Marmara is expressed by: S= 3.7 (δ18ow) (Rank et al., 1999). Sea surface oxygen isotope values varies by about 1.5 to 2 with latitude, decreasing from low to high latitudes.

17 Temperature estimates from Oxygen Isotope δ 18 O Composition The oxygen isotope ratio(δ 18 O ) of calcerous fossils depends on the temperature of calcification 1 corresponds to an apparent change in temperature of 5 C.

18 Marine oxygen isotope stages Glacial-interglacial cycles represented by even and odd numbers, respectively

20 Oxygen isotope values of different water masses in the Mediterranean Sea, Black Sea, and Sea of Marmara Sea δ 18 O ( ) Source Black Sea Surface waters (Feb. 95) Deep waters >500 m (March mean) Azov Sea Danube mouth (sea) Kerch Strait Danube (mouth) Dinyeper, Don Caucasus rivers Çoruh Black Sea meteoric water Eastern Med. (Feb 88) Surface Intermediate water Deep water Sea of Marmara Surface water (Mart 95) Deep water( >50 m,(june,95) >50 m (March, 95) (-2.1) (-3.4) (Mean.: ) (-1.73) (-2.23) (-2.5) (-3.8) ~ -5 ~-3 ~ (5.3) (-8.2) (-10) (-13) ~ (-7) (-8) (+1.57)-(+1.93) (+1.70)-(+1.94); Mean: 1.86 (+1.71)-(+1.87); Mean: 1.80 (-1.73) (+2.3) ; Mean: (ort.) (ort.) Rank et al. (1999) Nikolaev (1995) Rank et al. (1999) Nikolaev (1995) Nikolaev (1995) Nikolaev (1995) Rank et al. (1999) Nikolaev (1995) Nikolaev (1995) Nikolaev (1995) Nikolaev (1995) Pierre (1999) Rank et al. (1999) Rank et al. (1999) Rank et al. (1999)

21 Carbon isotopes Important for: Determining organic productivity Atmosphere-ocean carbon flux Tracing deep ocean currents in oceanic basins Differentiating between organic carbon of different origins Determining the source of organic matter in sediments

22 Size of the carbon reservoirs and carbon transfer between different resevoirs during the glacial and interglacial periods Carbon reservoir Carbon mass mol Ocean and atmosphere 310 Forests 6 Soil 20 Glacial-Interglacial carbon transfer Glacial-interglacial CaCO 3 transfer 9 9

23 CARBON ISOTOPES 13 C values of some organic matter Organic matter 13 C Primordial carbon (carbonatite, kimberlite, meteorite) Blue-green algea -8 to -22 Terrestrial C 3 type plants -25 to 35 Terrestrial organic matter -27 Marine CaCO 3-2 to +3 HCO 3-1 to 2 Atmospheric CO 2-7 Biogenic methane -70-5

25 C-isotope fractionation during the carbon cycle High productivity in surface waters: In surface waters low 12 C In planktic foram shell with high 13 C Deep waters: Low 13 C Low 13 C in Benthic foram The higher the organic matter production the greater the fractionation ( vertical carbon isotope gradient: Δ 13 δ C=δ 13 C planktic - δ 13 C benthic ) of C-isotopes between the surface and deep waters.

26 Formation of organic matter in aquatic environments: Photosynthesis Within the photic zone: plants (algae, autotorophic organisms) forms the organic carbon by photosynthesis: light 106 CO NO 3- + HPO H 2 O + 18 H + C 106 H 263 O 110 N 16 P O kcal Phytoplankton In surface waters various types of phytoplankton (blue-green algae, coccolithophore, diatom, dinoflagellate) establish the primary productivity. This the first step in the food chain. The other steps are the zooplanktons and higher forms of life (e.g., fish, bivalves) in water: Phytoplankton Zooplankton Fish and other higher organisms

27 Carbon cycle and transfer in the oceans For every 4 organic-c atoms used there will be 1 inorganic-c used for the CaCO 3 shells during photosynthesis

29 MD-2430 Examples

30 Core MD-2430 Sapropel Vidal et al. (in prep.)

31 Sperling v.d (2003)

32 Sperling v.d (2003)

33 Sperling v.d (2003)

35 B.ÇEKMECE-K.ÇEKEMECE SHELF

36 Line 14 Line 14

37 Ostrea bank with rare Mytilus, serpulite and vermes. Abundant forams (Brizalina and Globigerina) in a mud matrix Fossiliferous mud with abundant vermes, serpulite and gastropod shells in a mud matrix Mytilus bank with rare Ostrea and forams (Elphidium) in a mud matrix

40 Karadeniz de Holosendeki İklim Değişimi Kayıtları

Chronostratigrafi Stratigraphic unit Bese of sapropel(unit II/III boundary) Age (a BP) Method 7090±180 6600 7540±130 7800 5083 14 C 14 C 14 C 14 C Varve count Source Ross & Degens (1974) Calvert

41 Chronostratigrafi Stratigraphic unit Bese of sapropel(unit II/III boundary) Age (a BP) Method 7090± ± C 14 C 14 C 14 C Varve count Source Ross & Degens (1974) Calvert (1987) Jones ve Gagnon (1994) Arthur & Dean (1997) Degens et al. (1980) First Cooclith band 3450± ± C 14 C 14 C Varve count Ross & Degens (1974) Jones & Gagnon, 1994 Arthur & Dean, 1997 Hay et al. ( 1991) Last cocclith invasion and base of Coccolith Unit 3200± ± C 14 C Varve count Varve count Ross & Degens (1974) Jones & Gagnon (1994) Degens et al. (1980) Hay et al. (1991)

42 Sedimantasyon ve kütle birikim hızları

43 Oxygen and carbon isotopes Carbonate

44 Carbonate and organic carbon distributions West Black Sea East Black Sea Late Maunder Minimum ( ; Pister, 1994; Lutherbacher et al., 2001)

45 Çağatay v.d. (2002)

46 Heinrich events Çağatay v.d. (2002)

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