Light in the Oceans

• most life depends upon sun for light energy• for photosynthesis• autotrophs = producers - capture light energy

to make food (glucose)

pigments - capture light for plantsex: chlorophylls, xanthophylls,carotenes, phycobilins

• different plants have different pigments

red seaweed

green seaweed

brown seaweed

1. reflected - back to atmosphere• more waves, more reflected• unusable by plants

sun that reaches ocean surface:

2. absorbed - taken up by water, converted to heat• 65% absorbed in first 1 m depth• < 1% of light penetrates to 100 m (330 ft.) – in clear water• therefore autotrophs must be near surface

white light is made of all colorsof the visible spectrum

we see an object as a color because those color wavelengths reflect off of the object and into our eyes

• some wavelengths absorbed at shallower depths than others• in open ocean - blue penetrates deepest• different plants at different depths have different pigments to use differentwavelengths

selective absorption

red seaweed

green seaweed

brown seaweed

photo of red t-shirt at 50 feet depth

because of selective absorption - red objects do not appear red at depth – there are no red wavelengths to reflect

no flash flash

compensation depth

• depth at which rate of photosynthesis = rate of respiration

• phytoplankton above compensation depth make enough food

• phytoplankton below compensation depth starve

• waves often carry phytoplankton below compensation depth

Turbidity

• cloudiness of the water• opposite of water clarity

Turbidity

• measured using secchi disk• 1 m in estuary to 100 m in open ocean

Turbidity

• coastal waters – higher turbidity (= lower secchi disk depth)• increased suspended solids:

soil organic mattersewage plankton

dissolved substances• compensation depth is shallower• blue wavelengths do not penetrate as deep• water appears green and brown• get different phytoplankton species in coastal, estuarine, and oceanic waters

turbidity in tropicalwaters

turbidity in temperatewaters