Chemical Oceanography Exam 3 (Final)
Variations in cellular elemental ratios are ________ (i.e. "Redfield" is just an empirical average).
common
Marine N-fixation is primarily carried out by ____________.
cyanobacteria
Sources of Silicon to the ocean
- Rivers - Hydrothermal vents - Atmosphere (clay dust)
Where does marine denitrification occur?
Hypoxic, sub-oxic, or anoxic habitats
quantum yield (i.e. light absorption) formula (Φ)
# of reactions / # of photons absorbed
Microbial Growth Efficiency (MGE) equation
(Biomass Production) / (Biomass Production + Respiration) AKA Carbon Assimilation Efficiency
Microbial Carbon Demand equation
(Microbial C Production) / (Microbial Growth Efficiency)
Sources of "new" (i.e. external sources) nutrients to open ocean
- Advection from shelf areas (where rivers and sediments supply nutrients) - Physical mixing vertical diffusion from deep water, episodic upwelling - Atmospheric input, DIN, DON, trace metals, some P - N fixation (prokaryotic) N 2 NH 3 R - Vertical migration conveyor from deep i.e. diatoms etc. Whales & fish that feed at depth and poop at sfc
N-cycle Nitrogen assimilation processes
- Assimilatory NO3- reduction (reduced to NH3 in cells and then forms glutamate and glutamine) - Assimilatory NH3- uptake (forms glutamate and glutamine)
humic substances
- Complex, amorphous organic matter - humic acids + fulvic acids - significant terrestrial input from rivers, but most is destroyed on continental shelves likely due to photooxidation
N-cycle N2-generating processes
- Conversion of N compounds into non-reactive N - Denitrification - Anammox
N-cycle ammonia producing processes
- Conversion of organic or inorganic N compounds into NH4+ - organic matter degradation - DNRA
Mixing Depth governs exposure of surface plankton to PAR and UV-R. Why does this matter?
- Deep mixing gives lower dosage to surface plankton - allows recovery/repair from UV damage - Shallow mixing results in higher UV dosage for surface plankton, with less recovery time - Also affects surface nutrient and phytoplankton distributions
What limits PP at any given time or place?
- Depends on where/when - Bottom-up controls include input nutrient fluxes and light - Top-down controls include grazing and viral lysis
What can happen when a photon is absorbed by molecules?
- Electrons transiently jump to higher orbitals, then spontaneously fall to their original position - Molecule becomes "excited" and more reactive - Molecule becomes oxidized (loses electron to a receptor) - Molecule becomes reduced (steals electron from a donor)
What causes differences in the RKR ratio of N:P between the Pacific and Atlantic oceans?
- Excess N2 fixation in surface of Atlantic (which gets regenerated ultimately as NO3-) - Excess denitrification (NO3 removal) in Pacific oxygen minimum zones
How does UV radiation affect biology and chemistry in the surface ocean?
- Inhibition of photosynthesis - Inhibition of bacterial production and growth - Selection force for UV-resistant organisms, and those able to adapt by production of UV screens (i.e. Mycosporine amino acids) - Possible mutagen driving evolution? - Factor affecting viability of eggs and larvae of macroorganisms that reside in surface waters? - Possible synergism with pollutants (e.g. PAH's)
Influence of photochemistry on organic compounds
- Mainly driven by UV-Radiation (290-400 nm) - DOM (i.e. CDOM) is the main absorber of UV-R in seawater - UV-R absorption by CDOM causes alteration of DOM
Importance of photoreduction
- Maintains metals in surface waters - Allows for metal pool availability to phytoplankton
The natural ozone layer in the stratosphere absorbs UVB radiation, but it is slowly being destroyed. Why?
- Man-made chlorofluorocarbons - Some natural halocarbons sucj as methyl bromide
Important photolabile compounds in seawater
- Nitrate - Nitrite - Fe 3+ - DOM-humic substances - Anthropogenic pollutants - DMS
Examples of large scale eutrophication
- North Sea - Chesapeake Bay - Louisiana shelf - Black Sea - Sargasso Sea
Operational pools of carbon in seawater
- POM - includes not only carbon but also H, O, N, P, S etc. - DOM - dissolved organic matter (about 50% C by weight) - POC - refers only to the carbon - DOC - PIC - CaCO3 - DIC - Total CO2 (all forms)
Organic nutrient pools
- PON/POP (the pools of N & P that are bound in organic particles larger than the operational dissolved cut-off) - DON & DOP (the pools of N & P that are bound in organic matter that passes through the operational dissolved cut-off filter)
Factors influencing particles and DOM
- PP - Proximity to rivers and sediments
Factors that affect light absorption
- Particles: organic vs. inorganic - DOM: quality and quantity
Photochemistry affects:
- Photosynthesis & Bacterial growth (photobiology) - Biological reactivity of DOM (both increasing and decreasing its lability) - Molecular weight distribution of DOM - Mineralization (loss) of DOM - Production of CO2(aq) from DOM - Metal cycling and availability - via photoreduction etc. - Pollutant degradation
Organic carbon
- Reduced carbon - Includes hydrocarbons CH4, CH3-CH3, etc. and black carbon - Nearly all reduced carbon on Earth is biogenic
Importance of atmospheric inputs of nutrients
- Significant source of N - Wet/dry deposition from atmosphere is important source of trace elements (i.e. Fe, Zn, Mn, etc.) - Contribute to "deposition events"
Biogeochemist's rule #1
- What isn't there may be most important (i.e. Substances with low concentrations may be especially important in biogeochemical fluxes - their concentrations are low because they are desirable molecules to microbes)
Marine snow
- agglomerated organic matter - enriched with bacteria and protozoans - possible low oxygen conditions - elevated nutrients
Important classes of organic nitrogen
- amino acids , peptides - proteins - urea - amino sugars - humic acids - nucleotides - betaines - methylated amines
What facilitates vertical flux of POM?
- dead phytoplankton - fecal pellets - molt shells - fragments - mucous feeding nets - dead whales etc.
Sources of regenerated nutrients to open ocean
- excretion by organisms - microbial recycling of organically bound nutrients - Benthic Pelagic coupling (in shallow systems)
Sources of DOM in seawater
- exudates - death or lysis of cells - sloppy feeding - digestion
Factors that influence N-removal in estuaries
- freshwater residence time - marsh surface area - bioturbation (each of these enhance O2 transport to surface sediment layers, allowing nitrification w/ NO3 being denitrified)
Reasons for high carbon burial on the continental margins:
- high productivity - > high POM flux to benthos - high particle flux leading to faster burial rate - shallow depth - less organic matter degradation on descent - remineralization slower under anoxia
Importance of organic carbon burial
- removes atmospheric CO2 - removes some nutrient elements and trace elements - leads to petroleum, organic rich shales, and natural gas
What is affected by eutrophication?
- species composition - biomass - balance of O2
Methods of nutrient removal from euphotic zone
- uptake by photoautotrophic & heterotrophic bacteria - sinking of particulate matter - export of DOM, DON, DOP via downwelling and vertical mixing
N-cycle respiration processes
- using N compounds as e- acceptors for organic matter oxidation - Denitrification - DNRA
N-cycle chemoautotrophic processes
- using N compounds as e- donors and energy sources for fixing CO2 into organic matter) - Nitrification - Anammox - Autotrophic DNRA
Paleoreconstruction of PO4 3- concentrations is based on strong relationship between dissolved ____and ____.
Cadmium and dissolved inorganic phosphate (DIP)
F-ratio = _______ in oceanic zones.
0.1 - 0.2
F-ratio = _______ in coastal/shelf zones.
0.5 - 0.7
Ultimate sinks for macro-nutrients in ocean
1) Sedimentation of solid material and burial (i.e. N, P, Si) 2) Denitrification (N only - loss of useable nitrate or nitrite by conversion into gaseous N2/N2O
Inputs of nutrient to the ocean
1) Watershed (river) delivery 2) Groundwater 3) Atmospheric inputs 4) N-fixation
Anammox may account for _______% of oceanic N2 production.
15-30%
The RKR Ratio of N:P
16:1
Using δ 15 N, Paerl and Fogel found that atmospheric input contributed between _________ of new nitrogen to North Carolina estuaries and coastal waters.
26% - 70%
Atmospheric (Nr) deposition supports about ____ of global New Production.
3.6%
Secondary photochemistry
A absorbs light energy and becomes excited, but it then transfers the energy to receiving molecule B, forming excited-state B*, igniting chain reactions (A-> A* + B -> B* + A -> chain reactions)
Anammox (anaerobic, ammonia, oxidation)
A chemoautotrophic process that removes fixed nitrogen (i.e. it produces N2)
Superoxide anion (O2-)
A reduced form of oxygen that is highly reactive (occurs when when a molecule absorbs a photon and donates an electron to O2)
_____ is a major source of mineral dust to the Atlantic, Caribbean, and Gulf of Mexico.
Africa
Non-limiting nutrient elements required for PP
C, H, O, S
wavelength formula (λ)
C/v - C: speed of light in vacuum (3x10^8) - v: wave frequency (wave cycles/s)
What is a major reactant in photochemical reactions, even though it does NOT absorb light directly?
Molecular oxygen
Cause of eutrophication
Alteration of nutrient inputs, both in terms of quantity and quality (nutrient element ratios).
Eutrophication
An increase in the rate of supply of organic matter to an ecosystem.
The global distribution of opal silica overlaps with PP distribution, why?
Because diatom debris generally accumulates in sediments under high productivity regions.
______ is less thermodynamically favorable than denitrification (under standard thermodynamic conditions).
DNRA
The main chromophore in the ocean
DOM
Degradation of a typical phytoplankton cell
Dead or compromised phytoplankton cells breaks down in to simple organic matter
Potentially-limiting trace nutrients for PP
Fe, Co, and other metals/vitamins
What transition metals have primary photochemistry?
Fe, Mn, Cu
Major dust "events" are well documented and are important sources of mineral aerosols containing _________ and other metals.
Fe, N, P
Why does the revised Redfield ratio matter?
It contains more reduced carbon (e.g. lipids) which results in different photosynthetic and respiratory quotients with respect to O2.
Biogenic silica is undersaturated everywhere in the water column, why?
It is highly soluble in warm seawater and dissolves faster at higher temperatures.
What does it mean if a metal is photolabile?
It results in the photoreduction of metal and oxidation of the organic molecule.
The ozone hole over Antarctica has grown larger, allowing a larger flux of UVB radiation. Why does this matter?
Marine organisms are very sensitive to UVB radiation.
Chromophores
Molecules that absorb light energy
Potentially limiting macro-nutrients required for PP
N, P, Si
Denitrification influences estuarine _____ ratios.
N:P
F-ratio
New production / total production
Why is the marine N-cycle so complex?
Nitrogen is found in many different forms (organic and inorganic) and there is a significant redox chemistry for N containing compounds.
What is the most potent oxidant?
OH radical
Amorphous silica is also known as __________.
Opal or opaline silica
What prevents or slows down the dissolution of biogenic silica?
Organic coatings on live diatoms
Dissolved pore-water PO4 3- adsorbs to CaCO3 minerals, affecting ____________ in carbonate-dominated systems.
P-availability
Utilization of DOP is favored under extreme __________.
P-limitation
Although it appears that many marine ecosystems are N-limited, some areas appear to be _____ & _____ limited.
P; Fe
Regenerated production
PP sustained by internally recycled nutrients (e.g. NH4+, urea, or amino acids)
New production
PP that is sustained by external sources of the limiting nutrient (e.g. N).
How is long-lived material ultimately removed from the ocean?
Photochemical oxidation (breaks down DOM into CO2 and smaller molecules)
__________ is a major sink for refractory DOM in the sea.
Photooxidation
Large Kd = __________
Rapid extinction and shallow penetration
Action spectra
The rate of a reaction as a function of the wavelength
Ammonification
The release of NH4+ from organic matter during decomposition.
Marine denitrification
Respiratory use of nitrate as e- acceptor for organic matter oxidation; produces N2 gas and completes cycle started with N2 fixation
______ is required by diatoms and other SiO2 depositing organisms.
Si(OH)4 (because SiO2 is the anhydride of this)
The most abundant compound on the surface of the earth is _____ (but relatively low in seawater).
Silica (AKA silicon dioxide SiO2 or silicate)
Small Kd = ___________
Slow extinction and deep penetration
Purpose of the Redfield, Ketchum, and Richards (RKR) Ratio
Stoichiometry of "representative" organic matter based on moles
Microbial Carbon Demand
The amount of carbon microbes need to take up and process to achieve a certain biomass production
Where is the highest solar energy and highest total UV energy located?
The equator
Dissimilatory nitrate reduction to ammonia (DNRA)
Use of NO3- as electron acceptor for OM respiration produces NH4+
Primary photochemistry
When compound A absorbs light energy directly and is converted into terminal products (A -> B + C)
Apatite
a calcium-phosphate mineral
Light energy is __________ in seawater such that total light energy (irradiance) at a given wavelength __________ exponentially with depth into the water.
absorbed; decreases
80% of total atmospheric nitrogen (Nr) deposition is ___________.
anthropogenic
N cycle has been significantly altered by ______________________ such as industrial N fixation, and by burning of fossil fuels and biomass.
anthropogenic activities
Kd
attenuation coefficient AKA the fraction absorbed per meter depth
FeOOH and Fe-clays in sediments can be a significant reservoir of P because phosphate ions ___________ to iron oxide.
bind strongly
Strong arguments for P as the ultimate limiting nutrient for global ocean productivity because there is no ______________ like there is for N (nitrogen fixation).
biological source
DOC concentration __________ away from shore.
decreases
Flux of POM ___________ exponentially with depth.
decreases
Photodegradation also bleaches CDOM, which _______ its absorption and its photoreactivity.
decreases
Horizontal and vertical distributions of nutrients are controlled by _______________ and ___________.
density stratification & deep conveyor circulation
Most organic carbon in the sea is _________ or ________.
dissolved or colloidal (operationally dissolved)
The largest pool of organic matter in seawater is _______________.
dissolved organic carbon (DOC)
Light is a form of ___________________ with wave-like properties.
electromagnetic radiation
Breakage of the C-P bond in phosphonates requires a C-P lyase _______.
enzyme
At steady state, New Production ______ Export Production.
equals
The greater the overall sedimentation rate of particles, the _________ the fraction of surface primary production delivered to sediments.
greater
Even substances with low concentrations can have ____ carbon fluxes if the turnover rate constant is large (fast turnover).
high
POM concentration is generally ____ in the upper water column and euphotic zone.
high
As with other macronutrients, HiSiO4 increases with depth and is ______ in the deep Pacific than deep Atlantic.
higher
Energy of a photon equation (E)
hv - h: Planck's constant - v = C/λ
Vivianite
hydrated iron phosphate
Whales are just one example of how vertically migrating animals can influence ________________.
nutrient transports
Most of the combined nitrogen in the sea is ____ or _____.
nitrate; DON
Only when light is absorbed can photochemical reactions occur - if compounds are transparent to light, then_____ photo reactions occur.
no
If N* is less than 0, then there is _____NO3- than expected.
less
The longer the wavelength, the ______ energy in a photon.
less
______ travels faster than sound
light
Quantum yields tend to decrease at _____ wavelengths (less energy per photon).
longer
Much of the present global carbon burial (preservation) is in _______ environments.
marine
DNRA is ______ favored over denitrification at higher salinity, higher temperature.
more
If N* is greater than 0, then there is _____NO3- than expected.
more
The shorter the wavelength, the ______ energy in a photon.
more
Primary productivity and biomass patterns are controlled largely by ______ availability and fluxes, with ______ playing a role at the poles.
nutrient; light
Many areas of the ocean have high _________ and low ________ (HNLC).
nutrients; chlorophyll
Deep ocean DOC concentrations decrease along ________________.
ocean conveyor
Up to 15% of modern land plants biomass may be made up of phytoliths made of ___________.
opaline silica
Adsorption of organic compounds to inorganic sediment surfaces may play a role in ___________________.
organic carbon preservation
Major ocean denitrification in Eq. Pacific ________________; responsible for low N:P ratio in dissolved nutrients in this region
oxygen minimum zone
NH3 or NH 4+ (ammonia and ammonium) are both forms of the same chemical depending on _____.
pH
Dissolved inorganic P is present mostly as a form of phosphoric acid, but the predominating form depends on ____, ______, and _______.
pH, temperature, and pressure
Most P in organisms and DOP is present in oxidized form as ________________.
phosphate esters (e.g. nucleic acids, phospholipids, ATP, nucleotides, etc.)
When P is scarce. some phytoplankton produce sulfur- or sugar-based lipids instead of __________, sparing P for other cellular needs.
phospholipids
Electromagnetic energy travels in distinct packets called _______.
photons
In the case of secondary photochemistry, compound A functions as a _____________, meaning it absorbs light energy and then causes something else to react.
photosensitizer
What is a major sink for refractory DOM in the ocean?
photoxodation
84.4% of organic matter to open oceans is derived from ______________.
phytoplankton
Some areas of the ocean receive low dust inputs. This leads to trace element limitation of ____________ mainly by low iron (Fe).
primary productivity
Strong absorption means ____ attenuation with depth.
rapid
Within the visible bands, _____ wavelengths are absorbed rapidly with depth, while _____ wavelengths generally penetrate the deepest.
red; blue
Open ocean ___________ are highest in the euphotic zone and decrease with depth along with availability of labile organic matter.
respiration rates
Cyanobacteria can have some silica in their cells so contribution to total BiSO2 (biogenic silica) can be ________ in low H4SiO2 environments.
significant
Recent studies show clearly that ___________ limit productivity and biomass in Equatorial Pacific and the Southern Ocean HNLC regions because atmospheric deposition of metal containing dust is very ______.
trace metals (mainly Fe); low
N* should be _____ if NO3- is present at Redfield proportion to PO4 3-.
zero
Average age of DOC in surface water
~6000 years
