light in the ocean

Light in the Ocean

.. and its influence on photochemistry

This is why some people appear bright - until you hear them speak.

Light travels faster than sound.

Disclaimer – quote probably not attributed to Einstein

Light is a form of electromagnetic radiation – with wave-like properties

wavelength (λ) = C/ ν

where λ is the wavelength in meters, C is the speed of light in a vacuum (3 x 108 m s-1) and ν is the wave frequency (# of wave crests (cycles) per second)

Electromagnetic energy travels in distinct packets called photons. The energy in each photon is given by:

E = h where h is Planck’s constant (6.63 x 10-34 J s) and ν is the frequency (s-1).Since ν = C/ λ we can relate energy to wavelength:

E = hC/ λ Thus, the energy in a photon is inversely proportional to the wavelength (longer λ = less energy; shorter λ = more energy)

Units used during measurements of light

Einstein = 6.02 x 1023 photons i.e. 1 mole of photons

It is convenient to work with Ein since photochemistry is a quantum process (if the quantum yield is 1, then one mole of photons causes 1 mole of molecules to react)

Light photon flux – often given as μEin cm-2 s-1.

Photosynthetically active radiation (PAR) is often given in these units; A bright summer day has a solar photon flux of about 2500 μEin cm-2 s-1 (= 2500 μmol photons cm-2 s-1)

The rate of light Energy delivery is often given in Watts

1 Watt (W) = 1 Joule second-1

Light energy flux is given in W m-2

Wavelength-specific energy is often specified. That is, the energy at a certain λ (or from a range of λ i.e. PAR (400-700 nm))

Energy per mole of photons at specific wavelengths

0

1E-19

2E-19

3E-19

4E-19

5E-19

6E-19

7E-19

8E-19

280 380 480 580 680 780

wavelength (nm)

Jou

les

per

ph

oto

n

Short wavelength light (i.e. UV) has higher energy per photon!

UV-RVisible

Photosynthetically-Active Radiation (PAR) is ~400-700 nM

InfraRed

400 nm

Energy per photon at specific wavelengths

From Whitehead et al, 2000

Visible lightUV-R

No UV-C reaches Earth’s surface

Most incident solar energy is in the visible band!

Light penetration into the ocean

Light energy is absorbed in seawater such that total light energy (irradiance) at a given wavelength decreases exponentially with depth into the water

Total light energy

Depth (z)

Iz = Io e-Kd zThere will be a different Kd for each wavelength!

Iz = irradiance at depth z

Io = irradiance at surface

Kd = attenuation coefficient (m-1)

Absorbed Energy

Kd is the fraction absorbed per meter

What happens to this light energy?

Depth

Large Kd rapid extinction & shallow penetration

Small Kd - slow extinction with depth & deep penetration

Iz/Io (fraction of surface irradiance)

Light absorption (i.e. Kd,λ) will be affected by several factors – more later….

λ1

λ2

λ3

Within the visible bands, red wavelengths are absorbed rapidly with depth. Blue wavelengths generally penetrate the deepest.

The penetration of visible light (PAR) depends on the characteristics of the water, including phytoplankton abundance.

Spectral irradiance at depth in the ocean is measured by spectral radiometers

0 20 40 60 80 100 120

% of surface irradiance

30

25

20

15

10

5

0

305 nm

320 nm

340 nm

PAR

380nm

Spectral radiometer data for optically-clear water from the central Gulf of Mexico

Low UV wavelengths are attenuated rapidly with depth. Greater than 90% of UV-B (< 320 nm) is absorbed above 15-20 m.

Total energy in 400-700 nm band

The 1% PAR depth at this site was ~120 m

1% light depth for any wavelength is given by 4.6/Kd

That is Iz/Io = e-Kz or ln(Iz/Io) = -Kdz

ln(0.01) = -Kdz or 4.6/Kd= z1%

This is equal to the 10% irradiance depth

305


UV absorption properties vary among water masses

DOM is the main chromophore (absorber of light) in the ocean. More correctly, it is specific constituents of the DOM that are the chromophores.

Together these organic chromophores constitute the

Colored Dissolved Organic Matter (CDOM)

(also called chromophoric DOM)

CDOM (at high concentration) can give water a yellow color (Gelbstoffe) and a high optical absorbance, particularly in the UV part of the spectrum.

Tea colored, black-water rivers are very high in CDOM!

Waterparticles

Total

DOM

Wavelength (nm)

Abs

orpt

ion

coef

fici

ent (

m-1)

300 400350 450 500 5500.0

0.6

0.4

0.2

0.8

Absorption spectra for whole water, and the DOM, particulate matter, and pure water fractions for a coastal seawater sample from the mid Atlantic Bight.

From DeGrandpre et al, 1996

Light absorption by seawater is mainly by DOM!

Differences in light absorption/attenuation in different water masses is governed mainly by: Particles – organic and inorganic

DOM - quantity and quality

Influenced by primary production and proximity to rivers and sediments

With exposure to UV-R, CDOM becomes bleached and it losses its absorbance, thereby changing the A350 vs. DOC relationship

The optical absorbance of water is usually directly related to the DOC (and DOM) concentration – but this relationship varies from one water mass to another.

Abs350 nm

DOC conc.

River water

Shelf water

Ocean water

Seawater CDOM absorption coefficient for 370 nm light as a function of Chl a concentration in those same waters Chlorophyll a (mg m-3)

This study found that seawater absorption coefficients in these hyper-oligotrophic waters were lower than published values for pure water!

Photochemistry

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

When photon (light) energy is absorbed by molecules, a variety of things can happen.

• Electrons transiently jump to higher orbitals, then spontaneously fall to their original position (times scales of nanoseconds). This results in fluorescence with emission being longer than the of the photon absorbed (the excitation photon)

• Molecule becomes “excited” and more reactive A --> A*

• Molecule becomes oxidized (loses electron to a receptor)

• Molecule becomes reduced (steals electron from a donor)

For a primary process, compound A absorbs light energy directly and is converted into terminal products:

A B + Chν

For a secondary reaction, A absorbs light energy and becomes excited – but it then transfers the energy to a receiving molecule B, forming excited-state B*. This can go on and on …

A A* + B B* + A’ chain reactionshν

Where A* and B* are excited state species

In this case, A functions as a photosensitizer - it absorbs light energy and then causes something else to react.

Primary vs. Secondary Photochemistry

Example: DMS does not absorb light directly so no primary photolysis. DMS oxidation in the light, occurs via a photosensitizer (e.g. DOM or NO3

-).

If O2 reacts with excited molecule, highly reactive singlet O2 (1O2) can form

Molecular oxygen is a major reactant in photochemical reactions (though it doesn’t absorb light directly).

Superoxide can be converted to hydrogen peroxide (H2O2), either chemically or enzymatically (superoxide dismutase does this). H2O2 is also a strong oxidant and reactive form of oxygen.

H2O2 can undergo direct photolysis (with UV-R) or can react with Fe(II) to form OH radicals (OH), one of the most potent oxidants known.

If a photoactive molecule absorbs a photon and donates e- to O2, it yields superoxide anion (O2

-) a reduced form of oxygen that is highly reactive.

All these reactive oxygen species are formed in seawater via photochemical reactions!

Inorganic constituents in seawater are not generally photoreactive.

Several notable exceptions include:

Nitrate

NO3- + H2O + light NO2

- + •OH + OH-

Nitrite

NO2- + H2O + light NO + •OH + OH-

The specific photo-reactivity (per mole) of nitrite is much greater than for nitrate

OH radicals are about the most potent oxidants known!

Concentrations in Antarctic surface waters

Nitrate

Nitrite

15-30 µM

0.1 – 0.2 µM

Polar seas have very high nitrate concentrations!

This has implications for photochemisty & biologyNitrate and nitrite can range from 1-15 µM in temperate

waters, mainly in winter and spring. Even higher concentrations can be found in coastal waters & river plumes

319 - 333 nm

325 - 380 nm

Transition metals such as Fe, Mn & Cu have primary photochemistry

Fe(III) Fe(II)hν

From Rijkenberg et al. 2005. GRL

Surface irradiance

UV-A (320-400 nm) >60% 55%

Visible (400-700 nm) 30% 40%

UV-B (290-320 nm) 3.5 – 6.5% 1.8 – 3.0%

Depth integrated in water column

Percent contribution of different wavelength bands of solar radiation to photoreduction of Fe(III) colloids in Antarctic waters

More labile and biologically-available

Photoreduction (direct & photosensitized) is important in maintaining metals in surface waters and keeping some of the metal pool available to phytoplankton

Influence of photochemistry on organic compounds

• DOM (i.e. CDOM) is the main absorber of UV-R in seawater

• UV-R absorption by CDOM causes alteration of DOM

• Mainly driven by UV-R

CDOMAltered CDOM

hν+ photoproducts

CO2

CO

COS

H2O2

Low molecular weight organic compounds e.g. formaldehyde, glyoxylate, etc. (i.e. labile to bacteria!)

After

Kieber

Mopper

Miller

Moran etc

Photodegradation also bleaches CDOM, decreasing its absorption and its photoreactivity

Moran and Zepp, 1997, L&O

From Mopper and Kieber, 2000

Photochemical Blast Zone - some DOM oxidized

Deep water transit (= 1000 y)

NADW formation. Labile DOM is utilized in relatively short time - leaving old refractory carbon to make another circuit

Upwelling of refractory, old DOM

Little alteration of old, refractory carbon

Photooxidation as a major sink for refractory DOM in the sea

If ultra-refractory DOM has average age of 6000 years, and if ocean circulation time is 1000 y, then on average 16.7% of this old carbon will be lost each circulation cycle. If ultra-refractory DOM has average age of 6000 years, and if ocean circulation time is 1000 y, then on average 16.7% of this old carbon will be lost each circulation cycle.

Summary of Important photolabile compounds in seawater

Compounds which are photolabile

Products

Nitrate (NO3-) •OH, NO2

-

Nitrite (NO2-) •OH, NO?

Fe3+ Fe2+

DOM-humic substances H2O2, Low molecular weight acids and aldehydes, CO, CO2, COS

Anthropogenic pollutants Modified pollutants

DMS (dimethylsulfide) DMSO and other products

0 20 40 60 80 100 120

% of surface irradiance

30

25

20

15

10

5

0

305 nm

320 nm

340 nm

PAR

380nm

Quartz tubes

Optical Buoy - In situ incubations in natural light field

Incubated water experiences natural light field

Comparison of Photochemical and Biological DMS loss processes – Ross Sea Polynya, Terra Nova Bay - January 13, 2005

In situ irradiation

DMS consumption rate constant (d-1)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

De

pth

(m

)

35

30

25

20

15

10

5

0

Photolysis Bio consumption

Bio consumption from CTD samples

MLD

Conditions:

Shallow mixing, calm winds, cloudy am, sunny pm.

Photolysis

Bacterial production (nM Leu d-1)

0.0 0.5 1.0 1.5 2.0

Irra

diat

ion

dept

h (m

)

30

25

20

15

10

5

0

ArrayDark

DMSPd consumption (nM d-1)

0 2 4 6 8 10 12 14 16 18

30

25

20

15

10

5

0

DMS consumption (nM d-1)

0 2 4 6 8 10 12

30

25

20

15

10

5

0

In situ irradiation

How are the biological processes affected by exposure depth (UV radiation)?

MLD = 25m

Mixing Depth governs exposure of surface plankton to PAR and UV-R

Shallow mixing results in higher UV dosage for surface plankton, with less recovery time

Shallow Mixing

100

50

25

75

0MLD = 50m

Hypothetical UV-R penetration

Deep mixing gives lower dosage to surface plankton - allows recovery/repair from UV damage

Deep Mixing

t t

Dep

th (

m)

Mixing depth also affects surface nutrient regime and distribution of key phytoplankton e.g. N-fixers

UV Shade

National Geographic, April, 2010

Using Solar UV to disinfect drinking water

Our changing atmosphere – stratospheric ozone depletion and the increase of UV-radiation at the Earth’s surface

Stratospheric ozone depletion is Stratospheric ozone depletion is causing UV-R to going up causing UV-R to going up everywhere on Eartheverywhere on Earth

• Highest total solar energy and highest total UV energy are at the equator.

• Largest seasonal variability in UV-R occurs at high latitudes- like the Arctic and Antarctic.

The ozone hole over Antarctica enhances flux of UV-B at the sea surface

Marine organisms are very sensitive to UV-B radiation!

Spectral shift in energy under ozone hole conditions

Data from Palmer Station, 1993

Ozone in the atmosphere is measured in Dobson Units (DU).

Dave Kieber

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)

How does UV-R affect biology (and hence chemistry) in the surface ocean?

Metals (e.g. Fe, Mn) held in organic complexes including

• Humics

• EDTA

• Siderophores

are photolabile – resulting in photoreduction of metal and oxidation of the organic molecule.

This type of photosensitized metal photoreduction is more important than primary photo-reduction of the metals.

Photoreduction (direct & photosensitized) is important in maintaining metals in surface waters and keeping some of the metal pool available to phytoplankton

Only when light is absorbed can photochemical reactions occur – if compounds are transparent to light, then no photo reactions occur

AAIdt

dA

Specific absorption of actinic radiation – light absorbed per unit volume of water per unit time

Quantum yield

The rate of a photochemical reaction of A is given by:

Actinic = chemically-active radiation

The absorption of light is a quantum process

Φ = quantum yield = # of reactions / # of photons absorbed

If the concentration of the actual chromophore is not known, the apparent quantum yield (ΦA ) is reported. The ΦA for seawater reactions is usually << 1 (few reactions per photon absorbed)

The quantum yield for marine photochemical reactions is often much less than 1. For example, the quantum yields of H2O2 photoproduction range from 0.00003 to 0.001.

Quantum yields also tend to decrease at longer wavelengths (less energy per photon).

Open symbols are seawater

Figure from Moran and Zepp, 1997

Absorption of light in the sea

5-7 % backscatter

Absorption

reflection

> 95% of light energy reaching the ocean surface enters the water if > 20o. 5-7% of light that enters ocean is lost due to backscatter (water leaving radiance)

Total attenuation of light in aquatic systems

Scattering by particles

K = aw + ap + ao + ai + Sw + Sp

Total attenuation

Absorbance by water molecules

Absorbance by particles

Absorbance by organics

Absorbance by inorganic molecules

Scattering by water

Absorbance means light energy is absorbed by chemicals in the system. Molecules that absorb light are called chromophores

About 50% of absorbed radiation is infrared which heats the water.

About 50% of absorbed radiation is infrared which heats the water.

Practical considerations for UV-research

Optical properties of various lab materials

Optical quartz – transparent to virtually all wavelengths

Borosilicate glass (e.g. Pyrex, Kimax, Duran) - (variable – can cut off < 340 nm)

Teflon (FEP) – Transparent to most UV- but some scattering

Polycarbonate (cuts off < 340 nm)

Whirlpak polyethylene bags - Transparent to UV-R – convenient to use, but must check for contamination

Acrylics – different optical properties depending on type (see next slide)

Selective filtration of light wavelengths

Mylar D and UF-3 acrylic %Transmittance

0

10

20

30

40

50

60

70

80

90

100

270 300 330 360 390 420 450 480 510 540 570 600

Wavelength (nM)

% t

ran

smit

tan

ce

Mylar-D

UF-3 Acrylic

UF-3 (or UV-O) acrylic – cuts off < 400 nm (i.e. all UV-R)

Plexiglas-G – cuts off < 370 nm

Mylar-D – cuts off < 315 nm (i.e. UV-B)

The ozone hole over Antarctica increased through 2005 – letting in more ultraviolet B radiation

2004 Total Ozone Mapping Satelite (TOMS) ftp://jwocky.gsfc.nasa.gov/pub/eptoms/images/spole/Y2004/

Stratospheric ozone depletion affects the total flux of ultraviolet radiation (UVR) to the Earth’s surface, but has a bigger impact on UVB fluxes.

Natural ozone in the stratosphere absorbs UV-B radiation (290-320 nm)

The protective layer is being destroyed by man-made chlorofluorocarbons (CFC’s)

Natural sources of halocarbons (i.e. methyl bromide) also play a role in ozone destruction

Action Spectra - For photochemical reactions, the rate of reaction is a function of wavelength

(the type of dependency is governed by the light absorbance of the material or system)

Action spectrum

Wavelength (nm)

Rate of DMS photo-lysis per photon

290 400 400Wavelength (nm)

Rate of DMS photo-lysis

In daylight

290

Sunlight normalized action spectrum

More photons in UV-A

Peak activity near 350 nm

Cut-off FilterFull 305 320 345 380 395 Dark

DM

S lo

ss (

%)

0

20

40

60

80

100

10 m 150m

DMS photolysis is mainly driven by UV wavelengths

65% of photolysis caused by UV-A

35% by UV-B

Toole et al., GRL 2004

Bouillon & Miller, GRL 2004

Optical (nm)

Apparent quantum yield

0 100 200 300 400 500

k (

h-1

)

0.0

0.4

0.8

1.2

1.6

2.0

Nitrate (M)

0 100 200 300 400 500

DM

S lo

ss (

%)

0

20

40

60

80

100

Nitrite (M)

0 1 2 3 4 5

Nitrate (M)

A

B

High DMS photolysis rates in Southern Ocean waters are partially due to natural high nitrate concentrations (Toole et al., GRL 2004)

About 35% of the DMS photolysis attributed to NO3

-

The remaining 65% of photolysis was due to highly reactive CDOM

Natural NO3

-

conc.

Added NO3-

+Nitrite

+Nitrate

Influence of NO3- on

DMS photochemistry also documented in the sub-Arctic Pacific during an Fe-fertilized phytoplankton bloom

Bouillon and Miller, (GRL, 2004)

Photolysis rate given here as apparent quantum yield (AQY) at 330 nm.

NO3- drawdown in patch

Decreasing DMS photolysis rate constant with time

NO3-

drawdown in bloom

Rate constants for depth-integrated water column DMS loss processes at station M (Nov 11 &13, 2003).

Process rate constant (d-1)

Sea-air exchange 0.023

Biological consumption 0.083 - 0.20

Photolysis 0.5 - 0.71

Photolysis dominated DMS loss processes at the ice edge station, during pre-bloom conditions. Data from Toole et al. 2004 GRL

Summary of DMS photolysis in high latitude, nitrate-rich waters

• Toole et al., 2004 results – high photolysis rates in pre-bloom Southern Ocean waters compared to other ocean locations– partly due to nitrate, but also high CDOM reactivity

• Photolysis was major loss process in ice edge waters where bio and ventilation loss was low

• Mechanism still unknown – Bouillon (OH radicals vs. Toole (not just OH)

• DMSO yield from DMS photolysis ranged from 33-45% in pre-bloom waters

Strong absorption

Weak absorption

Strong absorption

PARUVR

Dow

nwel

ling

spec

tral

irra

dian

ce

Adapted from: Smith et al. 1992. Ozone depletion: UV radiation and plankton biology in Antarctic waters. Science 255: 952

Strong absorption means rapid attenuation with depth

Surface irradiance

Irradiance at depths indicated

Infr

ared

PA

R

0o zenith angle

79o

Earth

Larger zenith angle means longer path through atmosphere, and hence more UV absorption

atmosphere

UV energy, as % of total, decreases with greater sun angle


The quartz tube parade

Quartz tube retrieval – oh, so gentle

Leucine incorporation (nM h-1)0.0 0.1 0.2 0.3 0.4 0.5

Incu

bat

ion

dep

th (

m)

20

15

10

5

0

Biological DMS loss rate constant (d-1)0.0 0.1 0.2 0.3 0.4 0.5 0.6

Incu

bat

ion

dep

th (

m)

20

15

10

5

0

In situ quartz tube deployment - April 23, 2000Central Gulf of Mexico

Bacterial production and biological DMS turnover are strongly inhibited under surface irradiance conditions

Dark incubatedsample

Dark incubatedsample

Full spectrum light at depth

Full spectrum light at depth

Leucine incorporation is an index of bacterial protein production

In permitting the ozone layer to be destroyed and the intensity of UV at the Earth's surface to increase, we are posing challenges of unknown but worrisome severity to the fabric of life on our planet. We are ignorant about the complex mutual dependencies of the beings on Earth ad what the sequential consequences will be if we wipe out some especially vulnerable microbes on which larger organisms depend. We are tugging at a planet wide tapestry and do not know whether one thread only will come out in our hands, or whether the whole tapestry will unravel before us.

Carl Sagan, Billions and Billions, 1997

The quality of light is important!

Shorter wavelengths have higher energy per photon. These photons can cause reactions that would not occur (or would occur at slower rates) with longer wavelength photons.

This is why the UV-B part of the spectrum is important!

UV-B drives many photochemical reactions

UV-B also directly affects biological systems DNA absorbs UV-B directly, causing thymine-thymine dimers and other DNA damage. Harmful effects of UV are only significant if rate of damage exceeds rate of repair (see work of J. Cullen and co-workers). UV-A (320-400 nm) may also be harmful because there are more photons of this relatively high energy radiation

Chlorofluorocarbon gases increased dramatically in the atmosphere but now appear to be leveling off. Many CFC’s are long lived in the atmosphere and are potent greenhouse gases

CFC-11 is just one type CFC

http://lifesci.ucsb.edu/~biolum/chem/

Great animation on light generation and fluorescence

http://lifesci.ucsb.edu/~biolum/chem/

Important photoproducts in seawater

Compounds which are photochemically produced

Source

H2O2 DOM+O2

CO (carbon monoxide) and CO2 DOM – humic substances

COS (Carbonyl sulfide) Organic sulfur compounds

Low molecular weight acids and aldehydes (pyruvate, formaldehyde, acetaldehyde etc)

DOM

Reduced metals Fe3+ and Mn4+ organic complexes, especially humic complexes

DMSO DMS (dimethylsulfide)

Calculated spectral photolysis rate of dimethylsulfide in Antarctic seawater under ozone hole and non–ozone hole conditions.

A 37% increase in DMS photolysis is predicted under ozone hole conditions

The Antarctic ozone hole - 1995

Dobson unitsSource: NOAA TOVS satelliteDobson units (a measure of atmos. column ozone)

Ozone hole

From Mopper and Kieber, 2000

Gulf of Mexico

Mobile Bay

Specific rate of light absorption of chromophoric DOM (Ka) plotted as a function of wavelength for estuarine and oceanic water.

Note the differences in scales!

CFC’s catalytically destroy stratospheric ozone

Each molecule of CFC can destroy many molecules of ozone

This destruction is especially severe at the poles such that ozone holes develop, letting in much more UV-B than normal.

Ozone hole over a city for first time (from news story on MSNBC)

Chile’s Punta Arenasis first urban areato fall under hole

For two days last month the ozone hole, seen in purple, extended over Punta Arenas, Chile, located at the southwestern tip of South America.

In general, ozone depletion is greater at higher latitudes. Thus, the decrease near Seattle will be greater than near Los Angeles, while Miami will see the smallest depletion of the three US cities. However, southern cities also have much higher incidence of UVB light; even with less depletion, the net increase in UVB can be greater.

http://www.epa.gov/docs/ozone/science/marcomp.html

DMS Total loss rate constant - and Bacterial production

-25

-20

-15

-10

-5

0

0.0 0.2 0.4 0.6 0.8 1.0

DMS loss rate constant (per day)

Dep

th (

m)

light

dark

Leucine

Leu dark

DMS photoxidation rate constant - 35S-DMS in quartz tubes incubated in situ - Station 4

-25

-20

-15

-10

-5

0

0.0 0.2 0.4 0.6 0.8 1.0

Fraction of DMS converted per day

Dep

th (

m)

light

dark

High photolysis rates of DMS in surface layers may be offset by lower rates of biological consumption

Bacterial production scaled to dark DMS loss

Hydrogen peroxide

H2O2 + UV-R •OH

Other Photoreactive inorganic species:

Adapted from: Smith et al. 1992. Ozone depletion: UV radiation and plankton biology in Antarctic waters. Science 255: 952

Gamma X- rays

Ultraviolet Visible Infrared Radio waves

Electromagnetic spectrum

Wavelength (λ)

Energy per photon

Jargon: rays = photons = wavesAll are forms of radiation

UV-C 190-290 nm none reaches Earth surface

UV-B 290-320 nm energetic photons, but few reach surface

UV-A 320-400 nm less energy per photon, but more photons

PAR 400-700 nm photosynthetically active radiation

IR 700- >1000 nm Near Infrared (heat) (far IR is up to 300,000 nm)

Components of Solar radiation

UV-C UV-B UV-A

light in the ocean

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