Properties of Seawater

Monday we talked about properties of water (Table 7.2)- dissolves solids and gases readily (“universal solvent”)

Last time (Wednesday) we talked about dissolved solids (mostly salts)

Today: Dissolved Gases- gas concentrations in seawater changes through air-sea interaction- saturation occurs when amount of gas entering = amount of gas leaving- conservative and non-conservative - nitrogen, oxygen, argon, carbon dioxide, and “trace gases” (ppb)

Geography 104 - “Physical Geography of the World’s Oceans”

solubility of gasses in seawater increases with:- decreasing temperature (bubbles in boiling water)- decreasing salinity- increasing pressure (expansion of warm carbonated drink)

gases in atmosphere & ocean

atmosphere ocean

there are other “trace gases” (ppb)

Carbon Dioxide - very important for photosynthesis (aquatic plants)

Oxygen - very important for respiration (most aquatic animals)

Nitrogen - required by primary producers (marine plants) in forms such as nitrate (NO3

−) or ammonia (NH3). Biological cycling has a slight effect on the amount of nitrogen gas in sea water

Argon - chemically unreactive, must be “air-injected” (need hydrostatic pressure to mix)

Carbon

CO2 – both extremely soluble and abundant in seawater

non-conservative (produced by consumers, used by producers)

biological and physical “pumps” get carbon dioxide (a greenhouse gas) out of the atmosphere for long periods of time (1000’s of years)

ocean acidification - decrease in pH of the Earth's oceans, caused by uptake of carbon dioxide from the atmosphere. Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.179 to 8.104 (a change of -0.075)

oxygen carbon dioxide

dissolved gases Atlantic vs. Pacific

gas exchangephotosynthesis

respirationdecomposition

respiration

oxidation

Atlantic – more recent contact with atmosphere

By the time water gets to the Pacific significant respiration and oxidation have occurred.

- increasing CO2 favors formation of carbonic acid & bicarbonate - more H+ lowers pH leading to ocean acidification - probably negative impact on calcifying organisms - area of active research

marine carbonate system (physical pump)

2

Carbon used in photosynthesis, phytoplankton die and sink (biological pump)

amount of carbon in ocean is about 60 times that in atmosphere

natural & anthropogenic CO2 in the atmosphere

Keeling Curve

anthropogenic CO2 in the oceans

putting more CO2 in ocean would reduce impact of increased atmospheric CO2

…”A leak would slowly change the composition of the surrounding seawater, making it less suitable for the various creatures living there,” said Andrew Dickson, a marine chemist at Scripps who studies the effects of carbon dioxide in seawater but is not involved with the study. “A significant rupture might immediately kill off everything in the sediments and some of the organisms in the overlying waters.”

Oxygen (non-conservative)

non-conservative - produced by producers, used by consumers

hypoxia – low oxygen, or “dead zone” regions that can’t support life, both naturally occurring and human induced

anoxia – regions of no oxygen

oxygen and nutrient profiles

oxygen carbon dioxide

phosphate nitrate silicate

dissolved gases & nutrients: Atlantic vs. Pacific

anoxia, a dead zone

off Louisiana

Fertilizer causes phytoplankton “bloom”. Phytoplankton die and sink.Bacteria decompose dead phytoplankton using up oxygen.

dead zone off Oregon, summer 2002

O2 profile off Oregon – summer 2002

hypoxia

Readings for next time (density):- text, Chapter 7 pgs 113 to Solar Radiation (pg 126)- reader pgs 31 – 50 Density and Pressure in the Oceans

Get a start on first half of HW problems!

Announcement:Kristin’s office hours are 2:00 – 3:30 on Thursdays.