Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution November 1981
Description:
Radiolarians which settle through the oceanic water column were
recovered from three stations (western Tropical Atlantic-Station E,
central Tropical Pacific-Pi and Panama Basin-PB) using PARLUX
sediment traps in moored arrays at several depths. The taxonomic
diversities of the radiolarian assemblages in the sediment traps were
very high. A total of 420 taxa, including 23 newly identified taxa, were
found at the three stations; of these, 208 taxa were found at station E.
The polycystine radiolarians generally reach the sea floor with little
change in abundance or species composition, although slight skeletal
dissolution occurs throughout their descent. The phaeodarian
radiolarians, on the other hand, are largely dissolved within the water
column; only a few species reach the sea-floor and these dissolve rapidly
at the sediment-water interface. Most radiolarian skeletons sink as
individuals through deep water columns without being incorporated into
large biogenic aggregates. Because significant numbers of nassellarian
and phaeodarian species are deep-water dwelling forms the diversity index
of radiolarians increases with increasing depth in the mesopelagic zone.
The vertical flux of the total radiolarians arriving at the trap
depths (in x 103 individuals/m2/day) ranged from 16-24 (E), 0.6-17
(Pl), and 29-53 (PB). Of these on the average 25% and 69% of the
total radiolarian flux is transported by Spumellaria and Nassellaria,
respectively, while 5% is carried by Phaeodaria. The measured Si02
content of the skeletons averaged 91, 98 and 71% of measured weight for
Spumellaria, Nassellaria and Phaeodaria, respectively. The supply of
radiolarian silica (mg Si02/m2/day) to each trap depth ranged from
2.5-4.0 (E), 0.9-3.2 (Pl), and 5.7-10.4 (PB). The Radiolaria appear
to be a significantly large portion of the Si02 flux in 〉63 pm size
fraction and thus play an important role in the silica cycle. When the
radiolarian fluxes at the three Stations are compared with Holocene
radiolarian accumulation rates in the same areas it became apparent that
several percent or less of the fluxes are preserved in the sediments in
all cases and the rest is dissolved on the sea-floor. Estimated excess
Si which is derived from Si02 dissolution on the sea-floor is fairly
small relative to advective Si in the western North Atlantic and thus it
appears to be insignificant to show any deviation in a simple mixing
curve of deep water masses.
Weight, length, width, projected area and volume of 58 radiolarian
taxa were measured. The density contrast of radiolarians, relative to
seawater, generally falls between 0.01 and 0.5 g/cm3. The sinking
speed of 55 radiolarian taxa, measured in the laboratory at 3°C, ranged
from 13 to 416 m/day. Despite the wide variety of morphology between the
species, sinking speeds were best correlated with weight/shell among all
the possible combinations of the examined variables. The estimated
residence times of these taxa in the 5 km pelagic water column ranged
from 2 weeks to 14 months. Large phaeodarians reached the water-sediment
interface relatively quickly and ultimately dissolved on the sea floor.
Small-sized taxa dissolved en route during sinking.
The standing stock of 26 examined abundant taxa is on the order of 1
to 100 shells/m3. Total radiolarian standing stock ranges from about
450 shells/m3 at Stations Pl and E to 1200 shells/m3 at Station
PB. The rate of production of total Radiolaria is calculated to be 77 to
225 shells/m3 /day. The turnover time for these species ranges from
several days to one month depending on the species and the assumption of
the depth interval used for the estimation.
Description:
This thesis work has been supported by the National Science
Foundation, Submarine Geology and Geophysics Program, Grant OCE80-l9386
and the Woods Hole Oceanographic Institution Education Office.
Keywords:
Radiolaria
;
Fossil
;
Marine sediments
;
Atlantis II (Ship : 1963-) Cruise AII108-2
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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