Learning goals. Understand the processes controlling the concentrations and distributions of: Major solutes Dissolved gases Nutrients Trace elements

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1 Learning goals Understand the processes controlling the concentrations and distributions of: Major solutes Dissolved gases Nutrients Trace elements Evaporated seawater in bottom of five-gallon bucket Major components of seawater: Why is the ocean salty? Salinity: quantity (by mass) of dissolved solids in seawater - after carbonate is converted to oxide, bromide and iodide are converted to chloride, and dissolved organic matter is oxidized Usually expressed as g/kg, or o / oo, or psu (practical salinity units) Average ocean salinity: 35 o / oo Average salinity of deep water in Puget Sound: ~30 o / oo surface water: ~22 to ~30 o / oo 1

2 Major components of seawater and constancy of composition Cl -, Na +, SO 4, Mg 2+, Ca 2+, K +, HCO 3-, These constituents, plus hydrogen and oxygen (in water molecules), make up 99.99% of the mass of seawater. Measuring salinity 1. Chlorinity (salinity = x chlorinity (%o) 2. Conductivity 3. Refractive index (refractometer) Relative concentrations of these components are invariant throughout most of the ocean. Implication: Measure one, calculate the others, and determine salinity CTD: Comparison of river and seawater composition Conductivity Temperature Depth Average Average Ion River (mm) Seawater (mm) Oceanographer s main sampling device Could be called: CTDLTrDOChlA Water-sampling rosette or carousel HCO Ca Na Cl Mg SO K CTD photo from Sea-bird electronics Seven major solutes in seawater make up its salinity. Their relative concentrations do not match river water. 2

3 Density (g cm -3 ) Density (g cm -3 ) Effects of salinity on seawater 1: Freezing point depression, boiling point elevation (disrupts H-bonding, lowers vapor pressure) Freezing point of seawater (35%o) ~ deg C 2: Changes density pure water density: 1 kg/l seawater density (35%o, 20 deg C): ~1.024 kg/l common density units: 24 s t 3. Causes stratification (along with temperature) 4: Eliminates density-temperature anomaly (24.7%o, freezing temp = deg C) Fresh water Max density Max density Temperature ( o C) psu Temperature ( o C) psu Temperature ( o C) Variation in water density with changes in temperature and salinity (calculated using equation of state of seawater at standard pressure) Comparison of river and seawater composition Average Average Ion River (mm) Seawater (mm) HCO Ca Na Cl Mg SO K Approx. residence Time (Million years) > Residence time = Quantity of a solute in the ocean Rate of supply or removal Mg and sulfate removed at hydrothermal vents, but K? (reverse weathering) 4KAlSi 3 O 8 + 4H + + 2H 2 O Al 4 Si 4 O 10 (OH) 8 + 4K + + 8SiO 2 3

4 Removal mechanisms Evaporite formation, precipitation, coprecipitation, uptake by organisms, sorption onto particle surfaces followed by burial in sediments, scavenging in hydrothermal vent systems (Mg +, SO 4- ), reverse weathering (K) What else is dissolved in seawater? Gases Metals Nutrients Organic matter Gas concentrations in air and seawater Gas Chemical symbol % in air % in water Nitrogen N Oxygen O Argon Ar Carbon Dioxide CO Neon Ne Helium He Methane CH Krypton Kr Carbon MonoxideCO Nitrous Oxide N 2 O Xenon Xe Dissolved gases in seawater: Major gases: N 2, O 2, CO 2, Ar, etc Factors influencing dissolved concentrations in surface ocean (1) Concentration in atmosphere (2) Solubility Water temperature (cold temperature increases solubility) Salinity (high salinity reduces solubility) (Air-sea exchange leads toward saturation: conc=f[atm conc, solubility(t,s,p)] ) CO 2 : high solubility Carbonate system (Ocean s buffering system): CO 2 + H 2 0 H 2 CO 3 H + + HCO 3-2H + + CO 3 Carbonate content of the ocean 60x the content of the atmosphere. (Ocean strongly affects atmospheric CO 2 concentration) Below the air-water interface: (3) In situ production or consumption 4

5 Seawater carbonate system CO 2 pumps: solubility and biological Forms CaCO 3 shells Forms organic matter both can sink Solubility pump Higher CO 2 solubility + sinking of cold water means high latitude seawater takes up CO 2 Lower solubility in warm water + upwelling of deep water means equatorial seas release CO 2 into the atmosphere Biological pump CO 2 (as bicarbonate) is taken up by phytoplankton to form particulate organic matter (POM) and CaCO 3 during photosynthesis Some of this POM and carbonate will sink to deep water Fate of POM: -Most is oxidized to CO 2 (and carbonate) which can reach the surface again via upwelling. -Some POM is converted to dissolved OM -A small fraction is buried in sediments. Biological Pump Solubility Pump Respiration Photosynthesis High latitude Low latitude Spatial CO 2 air-sea exchange Flux into the ocean Flux out of the ocean Solubility pump accounts for ~ 90% of carbon stored in ocean Figure from wikipedia.com From Takahashi et al Deep-Sea Research 5

6 Spatial variation in biological pump CO 2 is taken out of the atmosphere by biological productivity From Takahashi et al Deep-Sea Research Parts of Hood Canal become dead zone Lack of dissolved oxygen leaves sea life gasping JOHN DODGE THE OLYMPIAN Portions of Hood Canal have turned into a dead zone for sea life this fall, according to area residents and state officials. Hundreds of shrimp, crab, small fish, rockfish and striped perch have washed ashore in the past week from the Potlatch area north to Hoodsport. A lack of dissolved oxygen in the water -- a chronic late summer and fall problem that appears to be worsening in the 60-mile-long fjord -- is to blame, according to the state Department of Ecology. The life-and death-struggle for marine life in the canal is a telling example of how human-caused pollution, an unusually dry summer and ocean conditions can upset an ecosystem already handicapped by poor water circulation even in the best of times. In most years, the dissolved-oxygen problem is worse at depths of 30 feet and lower, which allows most fish and sea life to find some breathing room near the surface. But this year, even the surface waters are starved for oxygen, Ecology oceanographer Jan Newton said. "The fish and other marine organisms just can't escape it," Newton said. Recent storms with winds from the south might have pushed the oxygen-rich surface water out of the southern end of the canal, she said. Hoodsport residents Bob and Donna Sund said scuba divers in front of their waterfront home have reported all sorts of dead sea life, including octopus and rockfish, since late summer. "We didn't see the dead fish last year like this year," said Bob CO 2 and O 2 profiles in seawater Southern Bering Sea Why would most surface waters in the ocean be supersaturated with O 2? Dissolved oxygen in the southern Bering Sea Profiles from MBARI.org 6

7 AOU = O 2 content at saturation minus measured O 2 content Water depth = 4000 m Chlorofluorocarbons as tracers of large-scale circulation Concentrations and ratios of CFCs in the northern hemisphere (Fine 2011) Units: pmol per Kg Figure from wikipedia.com Distribution of dissolved CFC-12 in the North Atlantic Ocean (Bullister, 1989) 7

8 Seawater age in North Atlantic Gas summary years Fine (2011) At saturation, gas concentration controlled by atmospheric concentration and solubility Solubility varies strongly with temperature Photosynthesis and respiration affect CO 2 and O 2 concentrations, particularly at depth CO 2 enters the deep ocean via the solubility and biological CO 2 pumps Gas concentrations vary in the deep ocean along the deep ocean conveyor (O 2, CO 2, CFC) Distributions of reactive solutes: Nutrients Liebig s law of minimums: Maximum population size, or production, or growth rate is controlled by one limiting factor (e.g., in the case of marine algae, a single nutrient or light) How are limiting nutrients affected by biological processes? Why are N or P thought to be limiting for algal populations? N: Amino acids, nucleic acids, chlorophyll, etc. P: membranes (phospholipids), nucleic acids, etc. Traditionally, two elements are considered to be limiting in coastal waters: N, and P. But, other elements, such as Si, Fe, Co, Zn and other trace metals might limit phytoplankton growth from time to time as well. Adding N and P to the photosynthesis equation: 106 CO NO 3- + HPO H H + C 106 H 263 O 106 N 16 P O 2 8

9 Depth (m) Redfield Ratios of elements Most particles in the open ocean are of biological origin. The ratios of limiting elements in the ocean tend to conform to the following ratio (by atoms) - C : N : P = 106:16:1 106 CO NO 3- + HPO H H + C 106 H 263 O 106 N 16 P O 2 Dissolved nitrogen, phosphorus and silica species in the ocean N Forms: DIN: N 2, NO 3-, NH 4+, NO, N 2, Organic N: Particulate organic N, dissolved organic N P Forms: DIP: HPO 4 (84%), H 2 PO 4-, PO 4 3- (DIP species depends upon ph: ph H) Organic P: Particulate and dissolved Slope 1/16 Elemental ratios can tell you about the nutritional quality of POM C:N, N:P Si Dissolved forms: H 4 SiO 4 (silicic acid) Si(OH) 4 (~ 97%), SiO(OH) 3 1- (remainder) Other dissolved forms: [SiO x (OH) 4-x x- ] Particulate forms: SiO 2. nh2 0 (opal) Dissolved phosphate versus nitrate From Broeker and Peng 1982 Trace metals in the sea Is the ocean becoming cleaner? Vertical profiles of nutrients: Depleted in surface waters due to biological uptake Regenerated at depth due to organic matter decomposition ( µm ) Nitrate Phosphate ( µm (µm) ) Nutricline Southern Bering Sea (Spring 2007) 9

10 Processes affecting the distributions of reactive trace elements Adsorption: elements with low solubility often stick to the surfaces of particulate material Biological incorporation: Some metals are of nutritional importance or mimic nutrients and are taken up by phytoplankton Zn and Cd profiles look like nutrient profiles, with removal in euphotic zone. (Together, these processes are referred to as sorption ) Precipitation: concentrations are low enough that this is not important Coprecipitation: Due to low solubility, many metals will coprecipitate Regeneration: Breakdown of particles can release trace elements back into solution Cu profile indicates removal at intermediate depths in the water column. Data from Bruland Figure from Broeker and Peng 1982 Types of trace element profiles and residence times (t) Nearly perfect correlations between Zn and Cd and nutrients indicate complete removal by phytoplankton and identical recycling processes at depth. Accumulated: t > 10 6 years Correlations between Zn/Cd and nutrients are better than the correlation between nitrate and phosphate. Recycled: t: years Scavenged: t < 10 3 years Data from Bruland Figure from Broeker and Peng

11 Online version of periodic table of elements in seawater Figure by Y. Nozaki Seawater sampling: CTD + Rosette CTD = conductivity, temperature, depth 24 1L bottles Sensors: CTD Dissolved O 2 Fluorometer Light meter Transmissometer Altimeter Nitrate sensor? Others? CTD photo from Sea-bird electronics Sampling and measuring trace elements 11

12 SOIREE 2 tons Fe SOFEx SERIES Evaporated seawater in bottom of five-gallon bucket 12