Midterm Review Flashcards
WOCE and GEOTRACES programs, key components and goals of each
WOCE: World Ocean Circulation Experiment. research cruises in main ocean basins in the 90s. Took measurements for temperature, salinity, carbon, nutrients, etc. Goal is to track changes associated with climate change
GEOTRACES: Similar program to survey the distributions of isotopes and trace elements (chemical elements that were not previously surveyed) Goal: to fill in a lot of the gaps that we had in our measurements
Carbon reservoirs, relative sizes of key ocean pools vs atmosphere
Ocean vs atm
39,000 vs 750 GtC
MOST IS IN DEEP OCEAN
Atmospheric CO2 concentrations, pre industrial, current, glacial period
Pre industrial: stable for thousands of years ~280 ppm
Current: recently exceeding 400 ppm
Glacial period: ~80 ppm lower, much of this carbon was likely stored in deep ocean
IPCC Assessment Reports (AR5 AR6), CMIP set of model experiments
2.5 best case scenario
6-8 business as usual
Most things are projected to 2100 but he thinks they should be to 2300 because after 2100 is when things start to dramatically change in the ocean
Who write the IPCC
Working scientific experts in each country write the IPCC (government and universities)
Density gradient
Density is a function of temperature and salinity
-density increases as temperature decreases
-density increases as salinity increases
Pycnocline
A sharp change in density with depth. There is typically one at the base of the surface mixed layer
Thermocline
Change in temperature with depth
Halocline
Change in salinity with depth
Stratification
How rapidly density in increasing with depth
Vertical structure in oceans
Vertical mixing largely determines the flux of nutrients to surface waters. The depth of the surface mixed layer also controls the light level experienced by the phytoplankton
Surface mixed layer
Surface layer where rapid mixing results relatively uniform concentrations of passive tracers (i.e. DIC, nutrients, phytoplankton,etc.) can range from a few meters to hundreds of meters depth, with convective mixing
Stratification impact on vertical mixing rates
Stable or stratified water column -> weak vertical exchange
Unstable -> strong vertical exchange
The faster density increases with depth, the harder it is to mix nutrients into the Euphotic Zone.
Cause of connective mixing and associated nutrient entrainment
Convective mixing will result with strong vertical exchange. Often initiated when surface waters cool during winter. Connective mixing at mid to high latitudes is a key route for deep ocean nutrients to return to the surface.
External sources and sinks for ocean constituents
Key nutrients the main sources to the oceans are rivers and aerosol deposition and the main sink is burial in the sediments.
Rivers are a source of DIC to the ocean.
Hydrothermal vents are a source of iron.
Residence time, particle scavenging and the short residence time for iron
Residence time is the mean length of time spent in a reservoir
Iron residence time = 200 years
Iron is highly particle reactive, resulting in short residence times due to particle scavenging. Iron bound to ligands is scavenged more slowly than free Fe ions.
Coriolis force, effects on circulation, latitudinal dependence
Coriolis force: apparent force that deflects moving air/water masses
-right in north hemi
-left in south hemi
The strength of the Coriolis force increases with increasing latitude and is =0 at the equator.
EFFECTS ON CIRCULATION?
General surface wind circulation at ocean surface, (Easterlies and westerlies)
Easterly winds blow from the east to the west
Persistently westerly winds lead to northern Ekman transport of surface waters
Strong westerlies in the southern ocean
What processes drive ocean circulation in the ekman layer?
Upper few hundred meters?
Intermediate depth and deep ocean?
Directly moved around by winds.
Upper ocean influenced by geostrophic currents that are indirectly driven by the winds, through Ekman transport, and the resulting sea surface slope.
The intermediate depth and deep ocean are influenced by thermohaline circulation that is driven by small differences in density.
Ekman spiral, Ekman layer transport and relation to wind direction
The layer of the upper ocean encompassing the Ekman spiral is termed the Ekman layer and often corresponds to the surface mixed layer. The mean current over this layer will flow at right angles to the wind direction.
convergence and divergence in the surface ocean, effects on vertical water movement
Convergence pushes water to the center, which leads to downwelling.
Wind-driven divergence of surface waters pushes water away, leading to upwelling from deep waters coming back up.
geostrophic currents, a balance between what 2 forces?
How are they formed? Role of the winds
The coriolis force and horizontal pressure gradient
Ekman transport of surface waters sets up horizontal pressure gradients that drive geostrophic currents caused by the sea surface slopes. Once the waters start to go down the slope, the coriolis force will push it to a balanced position.
subtropical gyres: how does wind forcing lead to their formation?
Prevailing wind fields include a circular pattern around the subtropical gyres. These indirectly drive the gyre circulation.
western boundary currents vs. eastern boundary currents
Subtropical gyres have strong, narrow intensified western boundary currents and broad, weaker eastern boundary currents.
Antarctic Intermediate Water (AAIW), Subantarctic Mode Water (SAM)
Mediterranean Water, how/where is it formed?
AAIW: forms in the Antarctic Polar Frontal Zone in the Southern Ocean. forms from the surface waters getting pushed northwards by the Ekman drift in the Southern Ocean. They subduct under warmer, denser waters
SAM: forms near the sub antarctic. Form in the winter when you get deeper, cooler mixing and then some of that water subducts and sits on top of the AAIW
Mediterranean Water: forms in the northwestern Mediterranean. As the salty Mediterranean waters are leaving the mediterranean and interacting with the Atlantic waters, they are sinking until they reach denser waters. Then the mediterranean waters spread out laterally at that intermediate depth.
thermohaline deep ocean circulation
Deeper circulation that is a function of density and gravity.
Circumpolar Deep Water (CDW), where is it?, a mixture of what two water masses?
It circulates in the Antarctic Circumpolar Current and can be found in the deep Pacific and Indian basins.
CDW is a mix of NADW and AABW.
NADW vs. AABW formation (North Atlantic Deep Water, Antarctic Bottom Water)
NADW: salty waters brought north by the gulf stream are cooled during the winter, leading to deep convective mixing. The densest waters from that will become the NADW.
AABW: water underneath the sea ice gets saltier and saltier, which makes the water denser. Then they sink and flow along the bottom to form AABW
Differences: NADW gets dense by cooling and AABW gets dense by increasing salinity.
where do these deep waters eventually return to the surface ocean?
Wind driven upwelling at the Southern Ocean
role of NADW in the Atlantic Meridional Overturning Circulation (AMOC)
NADW sinks down and comes south at mid depths and upwells at Antarctic Divergence. Only the Atlantic basin.
role of AABW in the Southern Meridional Overturning Circulation (SMOC)
AABW are the densest waters so when it gets really dense next to Antarctica, it sinks all the way to the bottom of the ocean and then it starts moving north along the bottom, which is part of SMOC. all 3 basins.
How can chemical tracers (CFCs and 14C) constrain ocean circulation?
Once these chemical tracers get into the ocean, they’re very inert, they just move with the water. Using atmospheric and ocean concentrations of these tracers, we can determine when the water parcel was last at the surface when it absorbed them. This tells us how fast water is moving through the ocean. 14C is used for deeper waters and longer time periods because CFCs are only about 100 years old. 14C occurs naturally in the atmosphere so we use the half life and that’s how we know it takes about 1000 years to circulate in the ocean.
Nutrients, oxygen, and DIC concentrations along the deep water flow path, from “youngest” to “oldest” deep waters, how/why do carbon, nutrient, and oxygen concentrations change?
Nutrients and DIC concentrations are higher in deep/old waters because they are sinking to the bottom. However, oxygen is at a lower concentration in these older waters because it is consumed for the decomposition of nutrients.
How will climate warming impact the rates of overturning in AMOC and SMOC?
They will both slow down because the surface waters are getting less dense, so it gets harder to form deep waters.
ENSO, effects on ocean circulation and biology in the Pacific
Much lower primary production and chlorophyll concentrations due to less upwelling and upward flux of nutrients.
natural CO2 vs. anthropogenic CO2 in the oceans
Natural CO2: carbon that has always been there (pre industrial) before we started changing the atmosphere. This is most of the carbon in the ocean
Anthropogenic CO2: extra carbon that the ocean is taking up because human activity is adding it into the atmosphere
How is climate change affecting surface temperature and salinity at low latitudes?
They’re already salty and with climate change they get even saltier. Warmer temperatures lead to more evaporation.
How is climate change affecting surface temperature and salinity at high latitudes?
They get less salty because with increased evaporation, it is raining out at high latitudes so it is getting fresher.
How are these changes increasing stratification?
Warming surface waters will increase stratification.
How does increasing stratification affect nutrient supply from below?
Reduces nutrient flux to the surface.
atmospheric CO2 uptake and ocean acidification
Ocean acidification refers to the lowering of pH of the ocean, producing more hydrogen ions due to increase of CO2 uptake from the atmosphere.
air-sea gas exchange equilibration
where does gas go if one place has higher ppm
Flux depends on which concentrations are higher and lower
E.g. if atm is 450 ppm and ocean is 400 ppm gas will flow into the ocean because the partial pressure is lower in the ocean than in the air.
transfer/piston velocity (how does wind speed affect gas exchange?)
Strong winds would create a lot of turbulence on the ocean, the more turbulence, the more air bubbles and water bubbles enter so creates conditions where more gas can be dissolved. Pushes gas into the water
solubility pump and biological pump: key components and processes driving each
Solubility pump: also bring CO2 into the ocean mainly with circulation and the temperature effect on CO2 solubility. (cooling will have a flux of CO2 into the ocean)
Biological pump: primary production -> photosynthesis by the phytoplankton. A small fraction of that will sink out and be exported to the ocean interior. Moves carbon from surface waters to the deep ocean
photosynthesis-respiration equation
CO2 + H2O <-> (CH2O)n + O2
Photosynthesis: plants combine carbon dioxide, water, and light energy to form plant biomass
Respiration: oxygen is used to break down biomass to produce carbon dioxide, water and energy
Euphotic zone
thin layer at ocean surface (~100m) with enough light to support photosynthesis
Net Primary Production (NPP)
total carbon fixation by plants- their respiration costs. Organic matter supplied by NPP is available to support heterotrophic organisms
4 key limiting nutrients in the oceans
nitrogen, phosphorus, iron, and silicon
global satellite chlorophyll maps (where are highest/lowest concentrations found, why?)
Lowest chlorophyll concentrations are in the most stratified regions because they have the weakest nutrient outputs from below.
Highest chlorophyll concentrations in regions where the circulation brings more nutrients to the surface.
know equilibrium reactions/equations that occur when CO2 dissolves in seawater,
Atmospheric CO2 dissolved into the ocean
Dissolved CO2 + water -> carbonic acid
CO2 + H2O -> H2CO3
Carbonic acid turns into Bicarbonate ions OR hydrogen ions
Bicarbonate ions become carbonate ions OR hydrogen ions
pH buffering by bicarbonate and carbonate ions
If an acid is added, the carbonate ion will absorb some of the H+
If a base is added that removes some H+, some of the bicarbonate ions will release their H+
Low pH Carbonic acid -> high pH carbonate ion
H2CO3 -> CO3 2-
pH buffering by bicarbonate and carbonate ions
If an acid is added, the carbonate ion will absorb some of the H+
If a base is added that removes some H+, some of the bicarbonate ions will release their H+
Low pH Carbonic acid -> high pH carbonate ion
H2CO3 -> CO3 2-
pCO2 and CO2 solubility: influences of temperature, DIC concentration, salinity
Mostly temperature and DIC!
pCO2 increases with increase in temperature.
Colder water has higher solubility. Cold water can dissolve more carbon, lowers pCO2.
Warming increases pCO2 so it is harder to get CO2 into the ocean.
equilibration time for CO2 vs. O2
Most gasses have relatively short equilibration time O2 ~couple of weeks
CO2 equilibration time is ~1 year because CO2 reacts chemically with the seawater
B/c of this long equilibration time, the oceans are almost never in equilibrium with the atmosphere in respect to CO2.
CO2 chemistry in seawater and the ocean’s high capacity for taking up CO2
CO2 gas combines chemically with water, so the oceans have a great capacity to absorb CO2 more than other gasses
Heat transport in the oceans, influence on polar climate, and air-sea CO2 flux
Warm waters traveling north with AMOC.
The strongest ocean uptake from the atmosphere is where poleward transport leads to cooling of the surface waters and there is strong biological drawdown of CO2.
How is ocean heat uptake acting to slow the warming of the atmosphere?
Most of the heat added to the Earth System by rising greenhouse gas atmospheric concentrations has been absorbed by the oceans, greatly slowing the warming of the temperature.
How much has the upper ocean already warmed? impacts on sea level rise?
Mean warming of upper ocean waters of ~0.1 degrees C
Warmer waters are less dense so they expand, contributing to sea level rise
Seasonal sea ice patterns, trends, influence on heat and gas exchange with atmosphere,
Huge decreases in summer-season sea ice cover in recent decades, with dramatic minima in 2007 and 2012.
Sea ice cover is a strong barrier to air-sea gas exchange and a barrier for transfer of heat. If there is no ice the ocean will take in more gasses and heat.
How are sea ice cover patterns changing in the Arctic? in the Antarctic?
Arctic sea ice cover is declining most rapidly in summer months, but winter sea ice extent is also declining.
Climate models suggest that the Arctic will be ice-free during summer months by the end of this century under the strongest warming scenarios.
What are the key factors leading to sea level rise today?
-melting ice on land
-warming of ocean waters (as water warms density decreases=volume expands) (thermal expansion)
-changes in wind forcing and ocean dynamics
What are the biggest concerns about sea level rise in the future?
The Greenland ice sheet holds enough water to raise sea level by 7 m, putting most of Florida and large areas along the east coast underwater. Small island nations are particularly worried about this possibility.
influence of temperature, DIC concentration, and salinity on this C partitioning
Adding DIC to the oceans shifts C left.
Removing DIC shifts C right (DIC decreases and smaller fraction as dCO2)
Increasing temp shifts C left (increasing CO2 and pCO2)
Decreasing temp shifts C right (decreasing CO2 and pCO2)
the salinity effect comes from the dilution/concentration of DIC
How will the distribution of anthropogenic CO2 in the oceans change in 1000 years?
The anthropogenic CO2 will move through the deep ocean, eventually reaching the northern deep Pacific and Indian ocean basins.
How will the distribution of anthropogenic CO2 in the oceans change in 1000 years?
The anthropogenic CO2 will move through the deep ocean, eventually reaching the northern deep Pacific and Indian ocean basins.
~total anthropogenic CO2 uptake by the oceans (mid-1990s) since 1800,
48%
Wind driven upwelling. Where and why does it occur?
Wind driven upwelling occurs along the coast when wind blows parallel to the coastline. It occurs because the wind is pushing the surface waters away from the coast and water underneath has to replace it.
Coastal upwelling zones- where are major coastal upwelling regions
California
Ecuador
Peru
Wind forcing of the Antarctic circumpolar current and the Antarctic divergence
ACC driven by strong westerly winds in the Southern Ocean.
