Oceans OUTLINE. Reading: White, Chapter 15 Today Finish estuaries and particles, then: 1. The oceans: currents, stratification and chemistry

Transcription

1 Oceans OUTLINE Reading: White, Chapter 15 Today Finish estuaries and particles, then: 1. The oceans: currents, stratification and chemistry Next Time Salinity Exercise bring something to calculate with 2. the marine carbon cycle 1

2 Pb is flocculated more quickly than Zn too Also related to association with organics Faster removal: along river profile what do concentrations of Pb, Zn look like in river vs seds? River/estuary water: start Let s predict: Sediment: start high Pb content in sediments further upstream than the peak of Fe and Zn in many river-estuary systems. 2

3 10/4/17 Actual examples, other heavy metals Water flows through estuary, then north to Wadden Sea Metal groups: Fe-like group as baseline more floccable than Fe group not flocced group So, dissolved-particulate equilibria from estuary to near-shore environment determine concentrations Metal deposits in sediments Ex: Elbe River estuary, broad peaks in sediment metal concentration near station 8 = maximum point of infiltration of seawater through tides 3

4 Facts about the oceans v Represent >97% of the total mass of the hydrosphere. v Main repository on Earth for liquid water and its dissolved constituents. v Contain a significant amount of the worlds easily accessible carbon. v Where most of Earth s photosynthesis/respiration occurs. v Play a major role in regulating Earth's climate. v Oceans integrated ~100 million years of hydrospheric processes. v Overturn rate for the oceans is every ~ years in its present configuration and sea level. Accumulated and modified over Earth s history: Chemicals in the Oceans Salinity: PSU (Practical Salinity Unit, units of g/kg = parts per thousand, ) Origin of salts: -Rivers (main transport) Rain + CO 2 à H 2 CO 3 Si, Al, Na, K, Mg -Volcanoes Cl, S, CO 2 -Dust / Rain Fe, Si -Anthropogenic CO 2, P 4

5 Conservative elements: -major ions -are well-mixed -concentration varies with depth and location but ratio of conservative elements is essentially constant Chemicals in the Oceans Non-conservative elements: -Minor/trace elements -Abundances highly variable in the oceans Residence Time Residence time definition? T = Ocean amount / (Output) rate Conservative (Ma / (mg/l)): Na: 60 Myr Cl: 80 Myr Mg: 10 Myr / mg/l / mg/l / mg/l K: 6 Myr / 380 mg/l SO 4 :9 Myr Ca: 1 Myr / 905 / 412 mg/l mg/l Non-conservative (yrs) Mn: Fe: 100 / mg/l / mg/l τ res < 5x oceanic turnover rate 5

6 Conservative/Non-conservative & Salinity High salinity of seawater = high ionic strength (I = ½Σm i z i2» 0.7). (m = molality, z = charge) Salinity and temperature (=density) control stratification & circulation. Salinity controlled by major elements; were the major elements in seawater conservative/non-conserv., so salinity is conservative/nonconserv.? Salinity = conservative elements, so: marine (conservative ion)/(total salinity) ratios = constant Salinity 2 How to measure it? Current method: measure salinity through electrical conductivity What does it do to (sea)water? rayhaluchinc.com 6

7 Non-conservative ions Two important factors: ocean circulation, life overturn timescale: 2Ka Moving water interacts and changes composition Pick up nutrients as time goes on Photosynthesis only in top layer: large chemical differences vertically, affects nutrients and makes O2. Respiring organisms that don t need sun light: use up O2, some nutrients Deep Ocean Currents and Stratification: Stratification leads to excess photosynthesis in surface layer and excess respiration in deep layers => nutrient profile of composition vs depth Nutrients like NO 3-, PO 4 3-, Si (phytoplankton shells), micronutrients (Cd and Zn) reflect: 1. nutrient use in shallow oceans 2. age of the water (picks up as it goes) Use Old New 7

8 Ocean convection and oxygen Dissolved O 2 (Dox) profiles look like stratified lake except that O 2 reaches a minimum in intermediate depth waters: Deepest waters can be replenished by young deep water masses. 1 2 O Ocean Convection and chemical elements of life So, deep seawater masses change composition as they migrate through the oceans. Along this deep circulation flow path, they acquire: increased ΣCO 2 nutrients silica CA decreased O 2 ΣCO 2 and CA (carbonate alkalinity) also increase in older deep waters from sinking marine particulate matter, which affects CaCO 3 solubility and seafloor carbonate sediment preservation patterns Result: North Pacific deep waters have the highest nutrient content, highest ΣCO 2 and lowest dissolved O 2. 8

9 Upwelling Focused currents of deep cool, saline, oxygen-poor and nutrientrich waters are upwelled Cold water Cause: focused currents pulled away from the coast by the Coriolis effect: deeper water takes its place Upwelling Can see salinity, T and DIP come up from deep why? mid-water DOx is low, while shallow DOx is high why? More nutrients = more productivity = more sinking biomass = hydrocarbons = drilling for oil off California 9

10 The ph of sea water Seawater is very well buffered around ph ~ ) CO 2(gas) +H 2 OßàH 2 CO 3 ßàH + +HCO 3 ßà2H + +CO 2 3 atmospheric P CO2 ~ atm and carbonate formation buffer at ph = 8.4 2) photosynthesis-respiration [CO 2 + H 2 O CH 2 O + O 2 ] 3) element B (forms boric acid) B helps buffer sea water ph: ~ 3x HCO 3- concentration and B(OH) 3 + H 2 O B(OH) 4- + H + pk a1 = 9.00 C in the Ocean C = non-conservative; photosynthesis/respiration/circulation Pacific: deep inflow in the south. Return flow by upwelling and diffuse upflow Circulation resembles estuaries => estuarine circulation This circulation pattern affects nearly every aspect of the marine carbon cycle. Atlantic: has deep water formation from shallow waters: antiestuarine circulation 10

11 Where s the carbon? Approximate mass distributions of organic carbon: Type Concentration (μg/l) Total Reservoir (g) DOC (complex) x POC (dead bio) 20 3 x Plankton x Bacteria x Other, i.e., fish And Inorganic: DIC: ΣCO 2 (aq) PIC: CaCO x ug/l 2 ug/l Ratios of DOC, POC, PIC, and C:O mostly fixed by reactions Like photosynthesis/respiration Organic and Inorganic Carbon organic cycle of carbon: CO 2 air ΣCO 2 (aq) (CH 2 O) n or C 106 H 263 O 110 N 16 P inorganic cycle of carbon: CO 2 air ΣCO 2 (aq) CaCO 3 shells Linked through living and dead organisms 11

12 Carbon-Oxygen Relationship Rate of oceanic primary productivity is nutrient-limited - What does productivity do to O 2 in surface waters vs. deep water? - Where do you find high nutrient content within that last one? DOC stays dissolved, but POC settles out of the photic zone: Respirative decomposition of POC does what to O 2 in deep waters? Carbon-Oxygen Relationship What s in the picture? Oil sand with bitumen seeping out relevance: Balance of respiration vs photosynthesis? organic matter preservation globally limited Only appreciable C org preservation in high productivity zones What times in the geologic past was this balance different? Carboniferous 12