ultraviolet light
332
u
ultraviolet light ~UV light.
Ulvophyceae class of the green algae or Chlorophyta, which comprises most of the
green marine algae ranging from picoplankton to seaweeds of more than 1 m
long. In Caulerpa, cell walls are only formed to separate reproductive parts,
and numerous nuclei share the vegetative compartment. Ulva has one nucleus per cell. Most of the other species are intermediate in this respect.
UNCLOS I, II and III United Nations Conferences on the Law of the Sea (LOS), which
took place in 1958 (I) in Geneva, 1960 (II) also in Geneva and 1967-1982
(III) in New York-Caracas-Montego Bay. These conferences established an
internationally accepted Law of the Sea.
upwelling upward movement of deeper water under the influence of divergence
of water at the surface, usually caused by differences in Ekman transport. The
rise of nutrient-rich deep water into the euphotic zone stimulates phytoplankton
growth and, subsequently, that of zooplankton and nekton. Upwelling, or divergence, may be induced also topographically when currents pass islands,
peninsulas or seamounts, and eddies arise, but are especially induced by wind
patterns driving surface waters away from the coast (coastal upwelling). Major
upwelling areas, with large fish and squid populations (and fisheries) along
the west coasts of Mauritania and Peru are due to constant trade-winds
blowing parallel to the coast.
uranium (U), a radioactive metallic element (used, e.g., in nuclear weapons and
as fuel in nuclear power stations) with the atomic weight is 238.03. The uranium isotopes 23SU and 238U comprise 0.715 and 99.28% of natural uranium,
respectively. The concentration of uranium in seawater may be different in
various marine systems (estuaries, coastal seas, oceans), the average values
for oceanic waters around an overall mean of 3.3 flg 1-1, which correspond to
a radioactivity of 2.2 pCi 1-1. In the ocean 234U and 238U occur in dissolved
form and are mother isotopes of a family of radioactive daughters. The
radioactive decay series of 238U (234U) provide important time clocks for the
rates of oceanic processes.
Urochordata (syn. Tunicata) subphylum of the phylum Chordata. Together with the
subphylum Cephalochordata, they lack the characteristic backbone of higher
chordates (Vertebrata), but belong to the Chordata because during their embry-
332
u
ultraviolet light ~UV light.
Ulvophyceae class of the green algae or Chlorophyta, which comprises most of the
green marine algae ranging from picoplankton to seaweeds of more than 1 m
long. In Caulerpa, cell walls are only formed to separate reproductive parts,
and numerous nuclei share the vegetative compartment. Ulva has one nucleus per cell. Most of the other species are intermediate in this respect.
UNCLOS I, II and III United Nations Conferences on the Law of the Sea (LOS), which
took place in 1958 (I) in Geneva, 1960 (II) also in Geneva and 1967-1982
(III) in New York-Caracas-Montego Bay. These conferences established an
internationally accepted Law of the Sea.
upwelling upward movement of deeper water under the influence of divergence
of water at the surface, usually caused by differences in Ekman transport. The
rise of nutrient-rich deep water into the euphotic zone stimulates phytoplankton
growth and, subsequently, that of zooplankton and nekton. Upwelling, or divergence, may be induced also topographically when currents pass islands,
peninsulas or seamounts, and eddies arise, but are especially induced by wind
patterns driving surface waters away from the coast (coastal upwelling). Major
upwelling areas, with large fish and squid populations (and fisheries) along
the west coasts of Mauritania and Peru are due to constant trade-winds
blowing parallel to the coast.
uranium (U), a radioactive metallic element (used, e.g., in nuclear weapons and
as fuel in nuclear power stations) with the atomic weight is 238.03. The uranium isotopes 23SU and 238U comprise 0.715 and 99.28% of natural uranium,
respectively. The concentration of uranium in seawater may be different in
various marine systems (estuaries, coastal seas, oceans), the average values
for oceanic waters around an overall mean of 3.3 flg 1-1, which correspond to
a radioactivity of 2.2 pCi 1-1. In the ocean 234U and 238U occur in dissolved
form and are mother isotopes of a family of radioactive daughters. The
radioactive decay series of 238U (234U) provide important time clocks for the
rates of oceanic processes.
Urochordata (syn. Tunicata) subphylum of the phylum Chordata. Together with the
subphylum Cephalochordata, they lack the characteristic backbone of higher
chordates (Vertebrata), but belong to the Chordata because during their embry-