Article

Seasonal fluxes of silicoflagellates and Actiniscus in the subarctic Pacific during 1982-1984

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Abstract

A seasonal flux study of silicoflagellates and Actiniscus was conducted at subarctic Pacific Station PAPA (50N, 145W; water depth 4200 m) during September, 1982 through August, 1984 using PARFLUX high resolution time series sediment traps deployed at 1000 m and 3800 m depths. The time series sediment trap samples were collected for 4 to 16-day periods depending on the samples; most of the samples were collected for 14 to 16-day periods. From a depth of 3800 m, a total of 47 samples represents a nearly two-year continuous record of the fluxes of silicoflagellate and Actiniscus taxa. An additional 12 samples from 1000 m represent a 6-month period, providing synchronized time series samples with the deeper depth which is essential to understand particle sinking processes.Seven silicoflagellate taxa, several variants of silicoflagellates, and Actiniscus pentasterias (Ehrenberg) group were examined. A total of more than 32 × 103 specimens were identified to species level and counted in this study. Distephanus speculum (Ehrenberg) and Dictyocha mandrai Ling are the dominant taxa, generally contributing >75% of the flux assemblages. Considerable intra-annual and interannual flux variability was observed with the range of total silicoflagellate flux varying from 5 × 103 to 700 × 103 skeletons m−2day−1 during the two years. Seasonal flux patterns of D. speculum and its closely related taxa are internally consistent and they conform with the productivity signals shown by diatom, total mass, or opal fluxes. The seasonal flux pattern of D. mandrai exhibits its own unique late fall/early winter signals with most of the cumulative flux concentrated during this season in year 1.The sinking mechanism of silicoflagellates is large aggregates which sink faster than discrete specimens. Silicoflagellates generally sink faster than marine snow mediated diatom assemblages. The larger influence of fecal material may be responsible for the observed faster sinking speeds than those of diatoms. No significant dissolution of silicoflagellate assemblages occurs in the water column due to innate protection and to accelerated sinking. Most of the silicoflagellates supplied to the sea floor are subsequently dissolved, and only 1% of the total supply is preserved in the surface sediments, with considerably altered assemblages.

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... Quantitative slides for siliceous micro-and nanoplankton were processed using the residue 144 of the diatom slides prepared by Ren Pacific of Takahashi (1987) and Onodera and Takahashi (2007Takahashi ( , 2012. The illegitimate genus 162 ...
... Furthermore, S. speculum was found abundant in the Bering Sea (>60% in 278 sediment; Poelchau, 1976; >80% in sediment trap; Onodera and Takahashi did not show a clear seasonal variability (Fig. 2g). This species has also been found in the 305 subarctic (Takahashi, 1987) and tropical Pacific (Takahashi, 1991) melting season (Fig. 2g). Therefore, given its wide distribution, A. pentasterias is unlikely to 312 be an indicator of cold conditions. ...
... 3b). These results are in 267 line with the silicoflagellate composition from the nearby NAP site(Onodera et al., 2016)and 268 other studies, showing that S. speculum is a common species at high latitudes that dominates 269 the silicoflagellate assemblage of sinking particles and sediments north of the Subarctic Front 270 in the North Pacific(Poelchau, 1976;Takahashi, 1985Takahashi, , 1987; Onodera and Takahashi, 2005, 271 2012). Based on its distribution in the North Pacific, Onodera et al. (2016) inferred that S. 272 speculum might be indicative of mesotrophic to eutrophic conditions. ...
Article
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Siliceous planktons are valuable indicators of the environmental conditions in both modern and past marine settings. However, in contrast to diatoms and radiolarians, other siliceous micro- and nanoplankton in the Arctic Ocean have been rarely explored. In this study, silicoflagellates, endoskeletal dinoflagellate Actiniscus pentasterias and chrysophyte cysts were investigated in one-year mooring sediment trap material (from August 2008 to September 2009) collected in the Northwind Ridge, western Arctic Ocean. The silicoflagellate assemblage was dominated by Stephanocha speculum, accounting for > 71% of the total silicoflagellate composition. While S. speculum was overwhelmingly abundant in summer, S. medianoctisol and S. octonaria were more frequent during winter. The export fluxes of endoskeletal dinoflagellate A. pentasterias did not show clear seasonal pattern except for a peak value in September 2009. We suggest that high flux of A. pentasterias reflects nutrient rich environment at sea ice edge rather than cold under sea ice conditions. High fluxes of chrysophyte cysts were recorded in summer 2009 peaking in late July and early August, ∼10 times higher than in summer 2008. Peak of chrysophyte cysts and sea ice melting occurred simultaneously. In addition, observed encystment might be triggered by the population density, hence indicating a favorable environment for phytoplankton blooming. These siliceous micro- and nanoplankton provides information on the modern Arctic Ocean environment but requires further investigations to consolidate knowledge for robust use in paleoceanography.
... Silicoflagellates and other siliceous flagellates in sinking particles have been studied in both low-and high-latitude oceans (Takahashi 1987;Lange et al. 2000;Romero et al. 2002Romero et al. , 2009Rigual-Hernández et al. 2010;Onodera and Takahashi 2012); however, few studies are reported from the Arctic Ocean (Zernova et al. 2000). In the Arctic Ocean there are snapshot records of silicoflagellate occurrences in seawater and sea ice (Melnikov 1997;Takahashi et al. 2009). ...
... The maximum skeletal flux at station NAP was higher than that at station LOMO2. The mean silicoflagellate flux in our study was one order of magnitude lower than those in previous studies of silicoflagellate skeletal fluxes in the Bering Sea (Onodera and Takahashi 2012) and the eastern subarctic North Pacific (Takahashi 1987). At station AB in the southern Bering Sea in 1990-1994, D. medianoctisol had a mean relative abundance of 4 %, and D. octonarius was absent (Onodera and Takahashi 2012 The mean ebridian flux at station NAP was two orders of magnitude lower than that at station AB (53.5°N, 177°W, 3200-m trap depth, 3788-m water depth) in the Aleutian Basin of the Bering Sea for August 1990-July 1994 (14.7 9 10 3 skeletons m -2 d -1 ; Onodera and Takahashi unpublished data). ...
... The lower daily mean of diatom flux at station NAP (1.9 9 10 6 valves m -2 d -1 ; Onodera et al. 2015) than at station AB (52.6 9 10 6 valves m -2 d -1 for 1990-1998; Onodera and Takahashi 2012) might be related to the lower ebridian flux at station NAP. The sinking flux of A. pentasterias skeletons in this study was one order of magnitude lower than that at station AB in the southern Bering Sea for 1990-1994 (mean, 29.6 9 10 3 skeletons m -2 d -1 ; median, 25.2 9 10 3 skeletons m -2 d -1 ; Onodera and Takahashi unpublished data) and in the eastern subarctic North Pacific (Takahashi 1987). ...
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Spatial and temporal variations in major phytoplankton populations such as diatoms in the changing Arctic Ocean have been well studied, whereas only a few monitoring studies have been conducted on minor siliceous flagellates. To discern the relationship between hydrographic conditions and the spatio-temporal distribution of silicoflagellates, ebridians, and the endoskeletal dinoflagellate Actiniscus pentasterias, we analyzed seawater and bottom-tethered sediment-trap samples from the western Arctic Ocean. Silicoflagellates and ebridians were commonly observed in shelf waters around the southern Chukchi Sea in September–October during 2010 and 2013. However, one mesoscale patch with abundant silicoflagellates and ebridians was observed in the southwestern Canada Basin during September–October 2010. This offshore patch reflected an unusual occurrence of a mesoscale eddy deriving from the Alaskan Coastal Water. The active lateral transport of shelf materials by eddies was also evident in high silicoflagellate and ebridian fluxes at station Northwind Abyssal Plain (NAP) (75°N, 162°W, 1975-m water depth) in November–December during 2010 and 2011. The summer silicoflagellate flux at station NAP was mainly composed of Distephanus speculum. During the sea-ice cover period, except for July, silicoflagellates D. medianoctisol and D. octonarius were relatively abundant in the assemblage. The spike in D. speculum flux during July 2011 was observed with fecal pellets containing abundant silicoflagellates, suggesting a temporal silicoflagellate contribution to some kinds of zooplankton. The common occurrence of A. pentasterias in settling particles at station NAP during the winter may indicate their tolerance to cold water under sea ice.
... 10a-b). However, as evidenced by sediment-trap data of Takahashi (1987), silicoflagellate skeletons are less vulnerable to dissolution during settling through the water column than other siliceous microfossil groups, and the extremely large and heavily silicified skeletons may be more resistant to dissolution than diatom valves. Takahashi (1987) estimated that the percentage of silicoflagellate export flux preserved in the fossil record is 1.0-1.5%, ...
... However, as evidenced by sediment-trap data of Takahashi (1987), silicoflagellate skeletons are less vulnerable to dissolution during settling through the water column than other siliceous microfossil groups, and the extremely large and heavily silicified skeletons may be more resistant to dissolution than diatom valves. Takahashi (1987) estimated that the percentage of silicoflagellate export flux preserved in the fossil record is 1.0-1.5%, which is similar to estimates of diatom taphocoenoses (0.6-6.0%) (Tappan, 1980). ...
... The most striking feature of the siliceous microplankton assemblages at both Sites 748 and 749 is the dominance of ebridians and radiolarians, and the low relative abundance of diatoms. In sedimenttrap and plankton-tow data from modern waters, the abundance of diatoms typically exceeds that of ebridians by several orders of magnitude (Takahashi, 1987;Osawa et al., 2005), and diatom and silicoflagellate fluxes are generally higher than radiolarian flux (Takahashi, 1997;Seeberg-Elverfeldt et al., 2004). In the case of ebridians, a modern comparison, however, may not be reliable, since today the ebridians are regarded as a minor relic group (Hargraves, 2002), in contrast to their high diversity in the Paleogene (Tappan, 1980;Ernissee and McCartney, 1993). ...
Article
The Middle Eocene Climatic Optimum (MECO) is a major transient warming event that occurred at ~ 40 Ma and reversed a long-term cooling trend through the early and middle Eocene. We report the results of a high-resolution, quantitative study of siliceous microfossils at Ocean Drilling Program Sites 748 and 749 (Southern Kerguelen Plateau, Southern Ocean, ~ 58°S) across a ~ 1.4 myr interval spanning the MECO event. At both sites, a significant increase in biosiliceous sedimentation is associated with the MECO event. Rich siliceous planktonic microfossil assemblages in this interval are unusual in that they are dominated by ebridians, with radiolarians as a secondary major component. Silicoflagellates and diatoms comprise only a minor fraction of the assemblage, in contrast to siliceous microfossil assemblages that characterize modern Southern Ocean sediments. Based on our new siliceous microfossil records, we interpret two ~ 300 kyr periods of elevated nutrient availability in Southern Ocean surface waters which span the peak warming interval of the MECO and the post-MECO cooling interval. A diverse assemblage of large silicoflagellates belonging to the Dictyocha grandis plexus is linked to the rapid rise in sea-surface temperatures immediately prior to peak warmth, and a pronounced turnover is observed in both ebridian and silicoflagellate assemblages at the onset of peak warming. The interval of peak warmth is also characterized by high abundance of cosmopolitan ebridians (e.g., Ammodochium spp.) and silicoflagellates (e.g., Naviculopsis spp.), and increased abundance of tropical and subtropical diatom genera (e.g., Asterolampra and Azpeitia). These observations confirm the relative pattern of temperature change interpreted from geochemical proxy data at multiple Southern Ocean sites. Furthermore, rapid assemblage changes in both autotrophic and heterotrophic siliceous microfossil groups indicate a reorganization of Southern Ocean plankton communities in response to greenhouse warming during the MECO event.
... Poelchau (1976) showed that the latitudinal distribution of the Holocene silicoflagellates in the North Pacific sediments corresponds to latitudal temperature zones. Shitanaka (1983) also suggested that silicoflagellates are a salinity indicator, because the frequency of aberrant skeletons reflected the difference in salinity, more abundant in neritic waters than pelagic waters (e.g., Takahashi, 1987Takahashi, , 1991b. Takahashi et al. (1989) suggested that the interannual quantitative variability of siliceous phytoplankton flux, including silicoflagellates, at Station PAPA in the Gulf of Alaska was due to climate change. ...
... These results suggest that the oceanographic variability is also reflected in the silicoflagellate fluxes and assemblages. In the subarctic Pacific, silicoflagellate flux studies were carried out previously only in the eastern subarctic Pacific (e.g., Takahashi, 1985Takahashi, , 1987Takahashi, , 1989. The relationships between silicoflagellate flux and oceanographic variability were also discussed (Takahashi, 1997;Takahashi et al., 1989). ...
... We recognize that the use of generic names such as Dictyocha Ehrenberg 1837 and Distephanus Sto¨hr, 1880 has been discussed but not been settled to an acceptable form (e.g., Deflandre, 1952;Perch-Nielsen, 1985). Since the main purpose of this paper is to discuss the utility of silicoflagellate taxa as environmental proxies rather than to discuss their taxonomy, we follow the earlier classification used by Poelchau (1976), Takahashi (1987), and Takahashi and Blackwelder (1992) in this study. ...
Article
Time-series sediment traps were deployed during 1997–2000 in the northwestern North Pacific. The samples from 3000 m depth were investigated in order to study the silicoflagellate skeleton fluxes, the relationships with the geographical differences of their distribution, and their responses to temporal climate variations. At Station 50N (50°N, 165°E), located near the center of the Western Subarctic Gyre (WSG), subarctic-water taxa Distephanus speculum and Distephanus boliviensis dominated in the sinking assemblage. At Station KNOT (44°N, 155°E), located in the southwestern edge of the WSG, D. speculum also dominated throughout the sampled period. The warm-water taxon Dictyocha mandrai increased from the second half of 1998 to the first half of 1999, and the subtropical-water taxon Dictyocha messanensis also increased after the maximum period of D. mandrai flux. Not an obviously discernible seasonality was observed in the assemblages at Stations 50N and KNOT. At Station 40N (40°N, 165°E), at the south of the Subarctic Boundary, both the subarctic-water and the subtropical-water taxa dominated in winter and spring, and in summer and fall, respectively. The temporal assemblage variations at Station 40N significantly reflected the change of Sea Surface Temperature (SST) anomaly. This assemblage variation also implies which water mass, subarctic or subtropical, had more influence at Station 40N. The temporal successions of silicoflagellate assemblages at Station 40N are most likely due to the temporal oceanographic variability caused by global atmospheric changes. The differences of the seasonal flux pattern and the biogeochemical contribution of silicoflagellates at each station were due to the differences of ecosystem at each station.
... Their skeletons (size 20-80 ìm) are composed of biogenic opal which can be preserved in the sedimentary record. They generally represent a minor component of the total microplankton assemblage; they are considered to be indicators of water masses because they are influenced by changes in water temperature (Takahashi and Blackwelder 1992) and salinity (Takahashi 1987). In paleoceanographic studies silicoflagellates are used as a temperature proxy, as well as being reliable environmental indicators for high productivity and oligotrophic waters (Murray and Schrader 1983;Takahashi 1987;Onodera and Takahashi 2005;Barron and Bukry 2007). ...
... They generally represent a minor component of the total microplankton assemblage; they are considered to be indicators of water masses because they are influenced by changes in water temperature (Takahashi and Blackwelder 1992) and salinity (Takahashi 1987). In paleoceanographic studies silicoflagellates are used as a temperature proxy, as well as being reliable environmental indicators for high productivity and oligotrophic waters (Murray and Schrader 1983;Takahashi 1987;Onodera and Takahashi 2005;Barron and Bukry 2007). ...
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ABSTRACT: La Paz Basin is located in the southwestern sector of the Gulf of California, near the mouth of the gulf, and so it is influ-enced by waters in the gulf and from the equatorial Pacific Ocean. Sediments obtained from the basin contain a sub-millennial paleoceanographic and paleoclimatic record for the past 7256 years.Downcore abundances of coccoliths and silicoflagellates suggest that high paleoproductivity conditions were common in the sur-face waters of the basin due to upwelling and gyres. It was especially obvious in the lower part of core K47, but mainly between 3495and 2250 B.P. when taxa considered as high productivity and upwelling proxies (G. oceanica, “small” Gephyrocapsa, D. fibula var. robusta and O. pulchra) showed their highest abundances. These general conditions fluctuated throughout the time interval, with en-hanced incursions of tropical waters, similar to those during an ENSO events, observed at 5528 B.P. and 4500 B.P. but especially at3750 B.P. and in the upper part of the core.
... To date, no downcore studies of the relative abundance of silicoflagellates have been published on Holocene sediments from the middle to high latitude eastern North Pacific. Studies of North Pacific surface sediments (Poelchau, 1976) and sediment traps (Takahashi, 1987;Takahashi et al., 1989;Onodera and Takahashi, 2005), however, have established the ecologic preferences of numerous silicoflagellate taxa. Silicoflagellates have proven their utility in suggesting Holocene paleotemperature and upwelling changes in the Gulf of California (Barron et al., 2004(Barron et al., , 2005. ...
... Distephanus octangulatus is a subarctic silicoflagellate that is most common in cooler waters of the North Pacific including the Bering Sea and Alaskan Gyre (Ling, 1973;Poelchau, 1976;Takahashi, 1987). In general, D. octangulatus makes up less than 5% of the silicoflagellate assemblages of EW9504-17PC, ODP 1019, and EW9504-13TC with relative abundances increasing slightly to the north (Fig. 4). ...
Article
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Diatom and silicoflagellate records in piston core EW9504-17PC off southern Oregon, ODP 1019 off northernmost California, and piston core EW9504-13TC off central California reveal the evolution of the northern part of the California Current (CC) during the past 12,000 years. The early Holocene, prior to ~9 ka, was characterized by a relatively deep thermocline and warm sea surface temperatures, owing to enhanced northerly flow of subtropical waters comparable to the modern Davidson Current. Progressive strengthening of the North Pacific High caused intensification of the southward flow of the CC between ~9 and 8 ka, resulting in surface water cooling and increased coastal upwelling off northern California and southern Oregon. Strengthening of the CC possibly led to an intensification of the Southern California Countercurrent, causing a warming of surface waters in Santa Barbara Basin at ~7.6 ka that is suggested by oxygen isotope studies of planktic foraminifers. Between ~4.8 and 3.6 ka increased relative numbers of the silicoflagellate, Dictyocha aculeata, suggest deepening of the thermocline off northern California and southern Oregon during a period of enhanced water mass stratification in the Santa Barbara Basin. Modern seasonal oceanographic cycles evolved between 3.5 and 3.2 ka off California and Oregon, as evidenced by increased spring-early summer coastal upwelling and warming of early fall SST. Along the Pacific margin of North America between ~35 and 50 deg. N latitude, numerous marine and continental studies report a major climate transition between ~4 and 3 ka that may represent an increase in the expression of ENSO cycles. Further intensification of summer- spring coastal upwelling off California and Oregon appears to have occurred at ~1.5 ka.
... Particle increase in deep waters has also been observed by Leventer and Dunbar ( 1987), Takahashi ( 1987), Abelmann and Gersonde f 199 1) , and Sancetta ( 1992) in different regions of the world, and was explained as being a result of lateral advection, either downslope movement and high-velocity near-bottom currents or nepheloid layers. Bottom topography of the study area shows fluctuations of about 200 m over short distances (Wefer et al., 1991) which may have contributed to sediment redeposition along the seafloor, including the possibility of turbidites and other gravitycontrolled sediment deposition (see also GDP Site 662 in Ruddiman et al.,19%). ...
... As for diatoms, they may have been advected by downslope transport or midwater lateral transport from the productive coastal area. Because of their organic membrane, silicoflagellates are relatively resistant to dissolution (Takahashi, 1987) and, like radiolarians, show good preservation even when suspended in near-bottom waters (Lisitzin, 1972). This, together with their very low weight may allow individual silico~agellat~ skeletons to remain in suspension for extended time intervals and eventually to contribute to the apparent vertical flux. ...
Article
Sediment trap data from water depths of 853 m and 3921 m retrieved from the eastern equatorial Atlantic (01 °47.5′N, 11 °07.6′W; sampling time March 1, 1989, to March 16, 1990) reveal seasonal changes in the vertical flux of opal. Biogenic opal constitutes 3–20% of the total flux at 853 m and 10–19% at 3921 m. Important contributors to the opal fraction are diatoms and, to a lesser extent, silicoflagellates. At 853 m, the fluxes of both siliceous groups show a distinct seasonal pattern related to upwelling and the location of the ITCZ. The flux values are highest between March and April, and in August/September. The seasonal pattern with the spring and summer peaks can be recognized in the samples from 3921 m in a modified form: The flux curve is smoother and the time lag varies between 0 and 95 days. Higher flux values for diatoms, silicoflagellates and total particles in the lower trap suggests an additional source of material. Lateral advection of particles from the coastal regime seems to be an important factor at 3921 m, adding material at depth and distorting the original record. Also, freshwater diatoms were relatively important in the spring and winter samples at 853 m, and throughout the year at 3921 m, suggesting continental influence. A total of 202 diatom taxa were identified at both depths; only a few were responsible for > 50% of the total diatom assemblage. Nitzschia bicapitata dominated the assemblage. Differences in the relative abundances of strongly and weakly silicified diatom taxa between trap levels indicate dissolution in the water column. However, comparison between trap and sediment surface assemblages point to extreme dissolution at the sediment/water interface; approximately 98% of the siliceous shells are lost to the sedimentary record. Despite this loss, the changes between the surface sediment assemblages reflect the overlying hydrographic conditions of the surface waters.
... To date, no downcore studies of the relative abundance of silicoflagellates have been published on Holocene sediments from the middle to high latitude eastern North Pacific. Studies of North Pacific surface sediments (Poelchau, 1976) and sediment traps (Takahashi, 1987;Takahashi et al., 1989;Onodera and Takahashi, 2005), however, have established the ecologic preferences of numerous silicoflagellate taxa. Silicoflagellates have proven their utility in suggesting Holocene paleotemperature and upwelling changes in the Gulf of California (Barron et al., 2004(Barron et al., , 2005. ...
... Distephanus octangulatus is a subarctic silicoflagellate that is most common in cooler waters of the North Pacific including the Bering Sea and Alaskan Gyre (Ling, 1973;Poelchau, 1976;Takahashi, 1987). In general, D. octangulatus makes up less than 5% of the silicoflagellate assemblages of EW9504-17PC, ODP 1019, and EW9504-13TC with relative abundances increasing slightly to the north (Fig. 4). ...
Article
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Detailed diatom and silicoflagellates records in three cores from the offshore region of southern Oregon to central California reveal the evolution of the northern part of the California Current during the past 12,000 yr. The early Holocene, prior to ∼ 9 ka, was characterized by relatively warm sea surface temperatures (SST), owing to enhanced northerly flow of the subtropical waters comparable to the modern Davidson Current. Progressive strengthening of the North Pacific High lead to intensification of the southward flow of the California Current at ∼ 8 ka, resulting in increased coastal upwelling and relatively cooler SST which persisted until ∼ 5 ka. Reduced southward flow of the California Current between ∼ 4.8 ka and 3.6 ka may have been responsible for a period of decreased upwelling. Modern seasonal oceanographic cycles, as evidenced by increased spring–early summer coastal upwelling and warming of early fall SST evolved between 3.5 and 3.2 ka. Widespread occurrence of paleoceanographic and paleoclimatic change between ∼ 3.5–3.0 ka along the eastern margins of the North Pacific was likely a response to increasing ENSO variability in the tropical Pacific.
... There are exceptions to the warm and cool surface-water preference of extant Dictyocha and Distephanus. Dictyocha mandrai occurs in high percentages in the high-latitude North Pa cific (Poelchau, 1974) and Distephanus pulchra occurs at high abundance in low-latitude eutrophic environments (Takahashi, 1987). Although neither of these species were encountered in the present study, it is possible that some species of Dictyocha and Distephanus deviate from the predicted paleoenvironmental af finity. ...
Chapter
Silicoflagellate assemblages of ODP Leg 104 Neogene sequences are the basis of an interpretation of changes in the Neogene paleoenvironment of the Norwegian Sea. Fluctuations in the percentages of temperature and nutrient-sensitive taxonomic groups document major changes in sea-surface conditions. A brief, but distinct, cooling event occurred at 18.0-17.5 Ma which resulted in the disappearance of Naviculopsis. Following this early Miocene cooling a long period of increasing surface-water temperature occurred, leading up to a thermal high in the early middle Miocene (14.0 Ma). The early late Miocene (10.0-9.0 Ma) was distinctly cooler than the middle Miocene, but warmer than the remainder of the Neogene. Conditions between 13.0 and 10.0 Ma are unrecorded because of a regional hiatus, which is the earliest evidence for an end to the more temperate and stable conditions of the early to middle middle Miocene. A major plunge in temperatures occurred between 8.5 and 7.4 Ma and during the remainder of the late Miocene and Pliocene; from 7.4 to 2.65 Ma subpolar conditions prevailed. Silicoflagellates disappeared, except for sporadic occurrences, at 2.64 Ma with the beginning of dominant glacial sedimentation. Biogenic opal is absent in sediments younger than 0.76 Ma, indicating the dominance of glacial conditions with extensive sea ice. -Authors
... Even in the modern Bering Sea, the relative abundance of Dictyocha spp. in the total silicoflagellate assemblage is less than 1% during August 1990-June 1994 ( Onodera and Takahashi, 2012). On the other hand, the modern silicoflagellates in the eastern subarctic North Pacific show seasonal dominance of Dictyocha mandrai ( Takahashi, 1987). In addition, the relative abundance of Dictyocha in the modern Western Subarctic Gyre is less than 15% ( Onodera and Takahashi, 2005). ...
... For instance, in summer, C biomass estimates (not shown here) based on phytoplankton taxonomy of water samples suggests that the biomass of silicoflagellates was larger than the biomass of diatoms. Silicoflagellates are nanoplankton equipped with a hollow siliceous skeleton that are competing with diatoms for Si [Takahashi 1987] The seasonal analysis shows that, in spring, the net biological uptake rate of Si is larger than the rate of N (N: -796 mol s −1 , Si: -1460 mol s −1 , about 1.8:1) and the rates of N and P were again close to the Redfield ratio (N: -796 mol s −1 , P: -57 mol s −1 , 14:1). The Si:N ratio of uptake rates (about 1.8:1) and taxonomy data ( Fig. 5.13) suggest that spring diatoms were dominant and heavily silicified, compared to summer diatoms. ...
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During 2002–2006, a comprehensive set of observations covering physical, biological, radiative and atmospheric parameters was obtained from the southern Strait of Georgia (SoG), Western Canada by the STRATOGEM program. Monthly time series of estuarine layer transports over 2002–2005 were estimated using a time-dependent 2-box model in a formal inverse approach. These transports are then consistent with the temperature and salinity fields, as well as riverine freshwater inflow (R) and atmospheric heat fluxes. Uncertainty was analyzed by resampling observations using bootstrap methods. The transport time series were then combined with observations of nutrient concentrations to construct monthly time series of nutrient uptake for nitrate, phosphate, and silicic acid. Analysis of these time series suggests that the SoG estuarine circulation is not very sensitive to the seasonal changes of R. Comparison of the surface layer transport (U1) and R yields the first observational relationship between the SoG estuarine circulation and R. This relationship (U1=2.68 m2 s−2/3 × 103 R1/3 ) is consistent with estuarine theories. Although the flows change slightly with the freshet, a 5-fold change in R results only in a 40% change in U1. Based on the calculated sink of near-surface nutrients, net primary productivity is estimated to be 212 gC m−2 yr−1 , which is similar to values obtained differently in similar estuaries. Comparison of the nitrate and phosphate uptake rates suggests that the primary productivity (PP) is mainly new PP during spring and summer. Thus, PP is mainly controlled by the upwelling supply of nutrients through deep inflow and entrainment. The uptake of silicic acid (Si) is almost two times larger than the uptake of nitrate during diatom spring blooms, while it is similar during the summer blooms. Such a high Si uptake suggests that spring diatoms form heavier frustules or that heterotrophic silicoflagellates compete with diatoms for Si. Speculative considerations based on comparison of the estimated production rate of near-surface oxygen and new PP also suggest that the regenerated PP is small. In addition, the summer heterotrophic respiration might be in excess by as much as 2 gO m−2 d−1 relative to the net PP.
... The habitat preference of Dictyocha, from studies in the Northern Hemisphere, is ambiguous. Dictyocha is reported to prefer warm surface waters [Ciesielski and Weaver, 1974], yet Takahashi [1987] finds it common in the northern Pacific Ocean regardless of surface water temperature. The occurrence of Dictyocha in the relatively cold waters of the northern Pacific may be explained by transportation within warmer surface water eddies. ...
Article
In the modern marine environment the silicoflagellate genus Dictyocha is rare, or absent, south of the Antarctic polar front (APF); the genus Distephanus, in contrast, is dominant. In sediments recovered from ODP Site 1165, 1600 km south of the front, however, three intervals where Dictyocha is abundant are interpreted to represent Pliocene warm events. Comparison of our data with 's [1974] modern core top silicoflagellate relationship with sea surface temperature (SST) indicates that at Site 1165 mean annual SST was approximately 5°C at 3.7 Ma (event I), and approximately 4°C at 4.3-4.4 Ma (event II) and 4.55-4.8 Ma (event III). Event I represents a 5.5°C warming, and events II and III represents a 4.5°C warming relative to modern mean annual SST. Dictyocha is absent from other Site 1165 Pliocene intervals, which suggests that cooler SST (<2°C) prevailed. The warm events detected at Site 1165 may represent times when North Atlantic Deep Water production and ocean heat transport into the Southern Ocean exerted maximum influence.
... The production of biogenic particles is primarily concentrated in the upper most layers, with some exception in the deeper layers depending on taxa, of the oceans. Many, if not all, of the shell bearing plankton groups such as diatoms and radiolarians are produced attributing to certain environmental conditions and they can be transported to the sea-floor by means of aggregate sinking (e.g., Takahashi, 1986 Takahashi, , 1987a Takahashi, , b, c, 1995 Takahashi et al., 1989 Takahashi et al., , 1990 Honjo et al., 2008) and subsequently preserved as microfossils in sediments (e.g., Takahashi, 1994). Therefore, they can be well utilized for reconstruction of the past environmental conditions. ...
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... Distephanus pulchra was restricted to the northern sector of the area surveyed (north of 408S), whereas the other three had a more cosmopolitan distribution, ranging from 30 to 54-558S (D. messanensis, D. mandrai) and to 618S (D. speculum). These distributional patterns are in general agreement with the ecological preferences of these species reported for the South Atlantic (Eynaud et al., 1999) and for other areas of the World Ocean (Poelchau, 1976;Takahashi, 1987;Takahashi and Blackwelder, 1992). To establish biogeographic diatom-based zones along the transect, we performed a cluster analysis using depthintegrated diatom data (Fig. 5). ...
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Time-series fluxes of diatoms and silicoflagellates were measured nearly continuously at pelagic Station Papa in the northeastern subarctic Pacific during September 1982 through August 1986. Significantly large interannual flux variability was observed. In 1984 the fluxes were notably low relative to other years: either flux peaks were absent or slightly above the baseline values depending on taxa. Such flux suppression is attributed to changes in upper water hydrography. Within a limited physical oceanography data set a significantly shallower thermocline was observed during April 1984 than other years. This shallow and probable maximum winter mixing of 1984 is interpreted to have resulted in limited convective nutrient supply. Time varying export production of the siliceous phytoplankton, which can be continuously measured as vertical flux, is related with changes in the hydrography and thus the flux is a useful oceanographic proxy for mixed layer conditions.
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Surface water samples from the North Pacific and Bering Sea were collected and filtered during July-August 1999. The microplankton communities of these samples have been analysed by scanning electron microscopy. The results show that there are distinct differences in the distribution patterns of the major microplankton groups. In general, microplankton standing stocks were significantly higher around the Aleutian Islands and close to the coasts of Japan and America (ca. 105 cells/l) than in the open ocean (ca. 103 cells/l). The open ocean communities were dominated mainly by small nitzschioid pennate diatoms, although three bloom-like patches of the coccolithophorid species Emiliania huxleyi were also recorded. The coastal samples and those close to the islands were dominated by centric diatoms: Thalassiosira allenii in Tokyo Bay, Chaetoceros debilis, Thalassiosira oceanica. and par-males around the Aleutian Islands, and T. oceanica and Minidiscus spp. close to the American coast. In addition, chrysophyte cysts and Chaetoceros spores were more numerous near the Aleutian Islands. The tintinnid distribution also showed an interesting trend, with naked forms in the low productive waters of the central Bering Sea, diatom-covered forms close to the Aleutian Islands, and coccolith-covered forms in the bloom-like patches of F. huxleyi. This finding suggests that tintinnids merely use the available resources to build their Ioricae, rather than by selecting specific particles.
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To determine the influence of oceanographic conditions on silicoflagellate assemblages, sinking fluxes and composition of silicoflagellates were studied from August 1990 to July 1994 at two long-term monitoring sites: Station AB in the Bering Sea (53.5°N, 177°W) and Station SA in the northern subarctic Pacific Ocean (49°N, 174°W). Total silicoflagellate flux (TSF) increased annually in spring and/or fall at both stations. Interannual variation in the timing of the spring TSF increase was probably related to the depth of the mixed layer during winter and to the starting time of stratification. Composition of the silicoflagellate assemblage differed between the two stations. The assemblage at Station AB was composed almost entirely of Distephanus speculum, similar to the assemblage in the Western Subarctic Gyre. The temperate-subtropical genus, Dictyocha, occurred only sporadically. The assemblage at Station SA was more variable, reflecting changes in the climate–ocean relationships indicated by the Pacific Decadal Oscillation Index (PDOI). Dictyocha increased during the positive phase of the PDOI, due to intensification of the Alaskan Stream. In colder water, Distephanus with heptagonal skeletons were more abundant than hexagonal Distephanus. These results will be useful for paleoceanography studies of the area.
Article
Time series particle fluxes were monitored at pelagic Station Papa (50°N, 145°W) in the E subarctic Pacific from September 1982 through August 1986. Among 7 silicoflagellate taxa, Distephanus speculum and Dictyocha mandrai were dominant taxa which constantly represented >70% of total silicoflagellate assemblages. D. speculum flux trends, diversity indices and percent contribution to silicoflagellate assemblages reflect variability in upper water silicoflagellate production rate which is a consequence of hydrographic conditions. It is concluded that Stations Papa and C (49.5°N, 138°W) 600 km apart, are situated in the same oceanic province with similar ecosystems. -from Author
Article
Seasonal flux distributions of numerically dominant radiolarian species were studied using Particle Flux (PARFLUX) 1982-1984 high-resolution, time series sediment trap samples recovered from the eastern subarctic Pacific Station Papa (water depth: 4,200 m) in the Gulf of Alaska. Flux patterns of several major radiolarian species showed more temporally restricted seasonal maxima than those of siliceous phytoplankton groups, suggesting more confined seasonal flux signals than those of siliceous phytoplankton. These species showed significant flux reduction from year 1 to year 2 associated with an El Nino event, as did siliceous phytoplankton. On the other hand, fluxes of three major radiolarian subgroups and some other radiolarian species showed little change in timing or amplitude of seasonal flux patterns from year 1 to year 2 except for the presence/absence of summer maxima. This type of radiolarian flux signal is a reflection of recurring large changes in seasonal environmental conditions and, to a lesser extent, of response to the deviations of interannual amplitudes. Two generic pairs of radiolarian fluxes showed temporal niches which may have evolved due to dietary preferences. Biological competition may take place among species from different genera but not within a genus. Fluxes of juvenile and adult forms of two Pterocanium species were compared in order to understand their reproductive cycles. Reproduction appears to occur sporadically throughout most of the year and nonsynchronously among population members. The longevity of Pterocanium species was estimated to be several weeks. There are two separate radiolarian sinking processes; accelerated sinking via aggregates and discrete sinking. Smaller-sized species tend to sink faster due to aggregate incorporation than larger ones. Radiolarians are considered a good measure of productivity. The contribution of phaeodarians can be as high as 10% or more in total opal flux. Large-sized phaeodarian specimens are involved in this high percentage and play a significant role in silica redistribution within the water column since they dissolve quickly.
Article
Time series sediment trap samples were collected during October 1983 to August 1984 (second year) at 3800 m at station PAPA (50°N, 145°W water depth 4200 m) in the northeastern North Pacific. Components of diatom fluxes have been measured and compiled with previously published 1982-1983 records (first year). Most diatom species showed significantly lower cumulative fluxes in the second year than in the first. Second-year seasonal flux patterns were also notably different from those in the first year. Many of the differences are attributed to the second year's hydrographic change in density structure in the upper 100 m, resulting in a poor nutrient supply to the euphotic layer. The changes in the density structure were coincidental with the 1982-1983 El Niño disturbance. Such an observed flux decrease was analogous to notable changes in hydrography and biota reported elsewhere in the eastern subarctic Pacific which were reported to be due to the El Niño. Diatom fluxes clearly responded to this unusual climate change as well as to normal seasonal cycles. The value percentages of each species within total centric diatoms showed monotonous values thoughout year 2, when productivity was generally low. The percent values were similar to those of year 1's low production period, consistently indicating that these are low productivity signals. High diatom fluxes were accompanied by high percentages of Chaetoceros, suggesting high productivity signals. This strongly supports the contention that diatoms are sensitive climatic and productivity indicators. Maximum diatom carbon flux is mainly contributed by two taxa, Denticulopsis seminae, the smallest sized and most numerous taxon, and Rhizosolenia styliformis, the largest sized taxon. A sizeable contribution of carbon flux by R. alata f. gracillima was observed in year 1, but this was not repeated in year 2 due to the El Niño disturbance.
Article
Time-series sediment traps were deployed for five consecutive years in two distinctively different subarctic marine environments. The centrally located subarctic pelagic Station SA (49°N, 174°W; water depth 5406m) was simultaneously studied along with the marginal sea Station AB (53.5°N, 177°W; water depth 3788m) in the Aleutian Basin of the Bering Sea. A mooring system was tethered to the sea-floor with a PARFLUX type trap with 13 sample bottles, which was placed at 600 m above the sea-floor at each of the two stations. Sampling intervals were synchronized at the stations, and they were generally set for 20 days during highly productive seasons, spring through fall, and 56 days during winter months of low productivity. Total mass fluxes, which consisted of mainly biogenic phases, were significantly greater at the marginal sea Station AB than at the pelagic Station SA for the first four years and moderately greater for the last year of the observations. This reflects the generally recognized higher productivity in the Bering Sea. Temporal excursion patterns of the mass fluxes at the two stations generally were in parallel, implying that temporal changes in their biological productivity are strongly governed by a large-scale seasonal climatic variability over the region rather than local phenomena. The primary reason for the difference in total mass flux at the two stations stems mainly from varying contributions of siliceous and calcareous planktonic assemblages. A significantly higher opal contribution at Station AB than at Station SA was mainly due to diatoms. Diatom fluxes at the marginal sea station were about twice those observed at the pelagic station, resulting in a very high opal contribution at Station AB. In contrast to the opal fluxes, CaCO3 fluxes at Station AB were slightly lower than at Station SA. The ratios of Corg/Cinorg were usually significantly greater than one in both regions, suggesting that preferentially greater organic carbon from cytoplasm than skeletal inorganic carbon was exported from the surface layers. Such a process, known as the biological pump, leads to a carbon sink which effectively lowers p CO2 in the surface layers and then allows a net flux of atmospheric CO2 into the surface layer. The efficiency of the biological pump is greater in the Bering Sea than at the open-ocean station.
Article
Data on weekly to bimonthly particle flux collected by sediment traps in three environments show that forms of silicoflagellates do not have a simple and consistent relationship to either temperature or productivity of the overlying water column. Sites were located in the fjords of British Columbia, along a transect off the coast of southern Oregon, and in San Pedro Basin of the Southern California Bight. Either the “cool”Distephanus speculum or the “warm”Dictyocha messanensis may dominate at temperatures over a range from 10–19°C.D. speculum dominated high-productivity periods off Oregon, whileD. messanensis dominated during coastal upwelling events in the San Pedro Basin, regardless of surface temperature.Octactis pulchra showed no distinctive trend in the San Pedro Basin, the only locality where it was observed. The isolated presence ofD. speculum in the fjords, where mixed-zone salinity may be as low as 11‰, indicates a tolerance for hyposaline waters, but no other trends could be defined with respect to surface salinity.
Article
An assessment of the vertical flux of pelagic diatoms was conducted on PARFLUX sediment trap samples collected during September 1982–September 1983 at subarctic Pacific Station PAPA (50°N, 145°W; water depth 4200 m). A total of 24 time-series sediment trap samples were collected for 11- to 16-day periods during the year. Seasonal fluxes of 18 encountered taxa are reported. All of the taxa fall into one of five different types of seasonal flux patterns. Generally, taxa in Types 1–3 are indicators for high mass, opal, and organic carbon fluxes based on correlation analysis with mass and opal fluxes. Among them, Chaetoceros atlanticum, Rhizosolenia styliformis and Asteromphalus robustus are the best indicators for production. Unique signals from Coscinodiscus marginatus are present in the October–December high flux season and the January–March high percentage values.Based on flux maxima and minima and species components, samples from 1000 and 3800 m were cross-correlated. The correlations show that the two samples are generally offset by one sample interval of 2 weeks. The sinking speeds of diatoms are thus estimated to be approximately 175 m d−1 regardless of taxa, size, or morphology, invoking the necessity of aggregated and accelerated sinking. Diatom fluxes of various taxa measured at 1000 and 3800 m with one sample offset are generally nearly equal, implying that no significant dissolution takes place en route to the sea floor. A marked change was noted in the relative abundance of diatom species composition from the flux to surface sediment assemblages. For example, Denticulopsis seminae represents 87% in the flux of total diatoms compared to 30% in surface sediments. A significant alteration in percentages of diatom taxa place on the sea floor, with only 2% of the diatom flux being preserved in the surface sediments.
Article
Autotrophic and microheterotrophic plankton populations were monitored in the euphotic zone of the eastern subarctic Pacific during 6 one-month cruises in spring and summer, 1984, 1987 and 1988. Transmitted light, epifluorescence, and electron microscopy were used to identify, enumerate and estimate the biomass of size-populations of species. The 2–10μm size class dominated the biomass of both autotrophs and heterotrophs. The autotrophic flagellate, Phaeocystis pouchetii, was frequently observed in its non-colonial phase. Temporal variation in all the stocks was evident and could be explained only partially by the physical, chemical or biological factors investigated here. The general structure of the autotrophic community was similar to that in the North Atlantic, but major, unexplained variations between cruises occurred. Variation in mixed-layer depth and day length (but not variation in daily insolation) explained 25% of the variation in autotrophic doubling rate. Heterotrophic biomass comprised, in decreasing order of importance, non-pigmented flagellates, dinoflagellates, and ciliates. Ciliates rarely contributed more than 40% to the total. Microheterotrophic biomass rarely exceeded 30μg C 1−1 (avg 15μg C 1−1, 0–60m) whereas autotrophic biomass averaged 20μg C 1−1, 0–60m, and reached 74μg C 1−1 on one occasion, yet the grazing capacity of these microheterotrophs averaged 100% of primary production.
Article
To delineate potential water mass affinities, we investigated silicoflagellates from the region of Gulf Stream warm-core ring (WCR) 82B in the northwestern Atlantic. Silicoflagellates from 202 samples from N-S and an E-W transects across WCR 82B during late April were analysed. Shelf to Sargasso Sea transects, one completed in early May and the other in June 1982 were also examined. Eight to 11 vertical profiles to 200 m comprised each of the transects. Six taxa of silicoflagellates were found in the samples studied and a total of more than 8000 specimens were encountered. Three major taxa dominated standing stocks: Distephanus speculum, Dictyocha messanensis (intermediate-sized form) and D. mandrai. D. speculum, considered a cold-water taxon in the literature, showed a higher standing stock in the cooler high-velocity region (HVR) of the warm-core ring, continental shelf (SH) and slope (SL) waters. Fewer were present in the wanner ring center (RC), Gulf Stream (GS) and Sargasso Sea (SS). D. mandrai showed a similar distribution to that of D. speculum, but its preference for slightly warmer waters (>~10°C) was noted. In contrast, Dictyocha messanensis (intermediate-sized) and Distephanus pulchra, known to be warm-water taxa, were relatively abundant in the warm ring center. In contrast to standing stock data, ratios between cold- and warm-water taxa correlate well with temperature and salinity in the warm-core ring. Since these ratios are not effected by convective loss, they are excellent water mass tracers in this system. Distribution of the silicoflagellate taxa suggests that WCR82B April had a higher affinity with the Gulf Stream than the Sargasso Sea.
Article
Particle trap samples (VERTEX) from 4 locations in the northeast Pacific were used to compare centric and pennate diatoms with nassellarian and spumellarian radiolarians. The proportion of pennates and nassellarians were highest at VERTEX 3 from the northeast tropical oceans, off the west coast of Mexico. Colonial radiolarians were characteristic of warm, high saline waters from the southern edge of the north Pacific central gyre, north of Hawaii (VERTEX 4), while pennate diatoms were abundant. The subtropic oceanic Pacific (VERTEX 5A) had more pennate diatoms, while VERTEX (5C), in a coastal cyclonic eddy located west of California, had an even proportion of centric and pennate diatoms. Comparison of major faunas and flora at various oceanic sites of present siliceous sedimentation in conjunction with atmospheric, hydrographic and chemical data, can be helpful in reconstructing paleoceanographic and paleoenvironmental conditions of the past oceans throughout the Phanerozoic.
Article
We measured bacterial production and estimated the carbon consumption by bacteria in the mesopelagic zone (80–600 m) in the subarctic Pacific during May and August. Bacterial production was measured by leucine and thymidine incorporation. The two methods gave similar results. Bacterial production in the euphotic zone accounted for about 13% of primary production and in the whole water column for 20% (0–600 m). To bracket bacterial carbon consumption we made a lowest and highest estimate of bacterial production. The lowest estimate assumes zero isotope dilution for converting 14C-leucine incorporation rates into bacterial production and a 50% growth efficiency. In the mesopelagic zone, this estimate implies that bacterial account for 52 and 41% of the POC sinking flux as measured by sediment traps in May and August, respectively. The highest estimate, assuming two-fold isotope dilution of 14C-leucine and a 30% growth efficiency, yields bacterial carbon consumption values of 172 and 137% of the POC downward flux in both months. This indicates that bacteria are important, if not the major consumers of organic matter in the mesopelagic zone of the subarctic Pacific.
Article
The standing stock and species composition of phytoplankton (>10 μm) were studied using monthly water samples collected at Stn KNOT (Kyodo North Pacific Ocean Time Series; 44°N, 155°E) in the western subarctic gyre in the Pacific Ocean through June 1998 to June 1999 (except for January–April 1999) and January–February 2000. One-liter water samples were preserved in 1% neutrally buffered formalin. Identification and enumeration of phytoplankton were made with an inverted microscope.Nutrients did not appear to be depleted for phytoplakton growth during any season. The vertical distribution of phytoplankton was primarily restricted by the pycnocline, and the bulk of phytoplankton assemblage existed within the surface mixed layer. In July, however, some senescent cells were observed at 200 m. Phytoplankton abundance clearly showed a spring maximum (i.e. spring bloom) in May. The seasonal change in cell numbers, however, did not coincide closely with the change in chlorophyll a concentration. Centric diatoms, which were composed of Thalassiosira, Chaetoceros, and Coscinodiscus, dominated all year round, and showed temporal succession. Pennate diatoms (mostly Neodenticula seminae and Fragilariopsis) increased only during the spring bloom. Dinoflagellates (mostly Gymnodinium and Prorocentrum) were low in abundance, although they increased in summer when the phytoplankton standing stock was low. Silicoflagellate abundance was extremely low.Comparing the annual species composition of phytoplankton between Stn KNOT and Stn P (50°N, 145°W) in the Alaskan Gyre, there was a remarkable difference between the two sites. The phytoplankton assemblage at Stn P is characterized by a high abundance of Rhizosolenia alata and low abundance of Thalassiosira. In contrast, Thalassiosira dominates at Stn KNOT during most seasons.
Article
The observations of phytoplankton pigment by the former Coastal Zone Color Scanner for offshore areas of the subarctic Pacific and the western Bering Sea were reprocessed with attention to electronic overshoot. The data comprise 1979 to mid-1986, with two to three years of good coverage early in the period. Means for the individual days for seven large offshore `boxes' in each of the eastern and western subdivisions are depicted and evaluated, as are some surface observations of chlorophyll a and nutrients from ships. Basically, the entire deep-water region is a High Nutrient (nitrate)/Low Chlorophyll (HNLC) regime, excepting the areas off Washington/California and Hokkaido. Eastern and western subarctic including the deep Bering Sea do not differ in respect to the seasonal patterns of phytoplankton. Spring and summer blooms are absent throughout. Apparently, the winter production of phytoplankton is high enough also in the west, in spite of a deeper mixed layer, to maintain enough microzooplankton to suppress these blooms. The seasonal pattern of pigment appears to have been unaffected by the interdecadal regime shift of 1976/1977. This holds probably also for the concentrations, so that satellite observations of pigment will tell little about such shifts. The mechanism leading to rare autumn blooms in some boxes, relatively close to the continents, is unclear. In place of relaxation of grazing pressure from seasonal downward migration of larger zooplankton, a case is made for seasonally blown ash from volcanic eruptions as a source of iron, which increases algal division rates. Lack of sufficient size-fractionation data for phytoplankton in terms of chlorophyll is a serious impediment to understanding the seasonal phenomena.
Article
Seasonal and vertical flux variations of coccolithophorids, discrete coccoliths, silicoflagellates, ebridians, and diatoms were investigated using time-series sediment traps deployed in the central Black Sea for 2 years from September 1989 through August 1990 (Year 1) and from October 1990 through September 1991 (Year 2). The following marine plankton groups were not observed during the enumeration: dinoflagellates, radiolarians, planktonic and benthic foraminifers, and pteropods. High fluxes of coccolithophorids, discrete coccoliths, and silicoflagellates occurred from September to December in Year 1 and October to December in Year 2. High ebridian fluxes occurred during short periods from October to November in Year 1 and from February to April in Year 2. High diatom fluxes occurred from September to January in Year 1 and from October to April in Year 2. The seasonal variations and magnitudes of most plankton assemblages were similar between the Shallow trap (at a depth of 400 m) and the Bottom trap (at a depth of 2090 m) suggesting that the plankton shells settled at a rate of 60 m d−1 or greater without significant loss or lateral input. The exception was the diatom flux in Year 2, which was offset by approximately 2 months between the Shallow and Bottom traps, suggesting a sinking speed of approximately 38±18 m d−1. The slower setting speed is attributed to Pseudo-nitzschia spp., which was the dominant diatom taxon in Year 2. Maximum flux magnitudes of each plankton assemblage were on average two times greater in Year 2 than in Year 1. Emiliania huxleyi, Distephanus pulchrus, and Pseudo-nitzschia spp. dominated the fluxes of coccolithophorids, silicoflagellates, and diatoms, respectively. Significant changes in taxonomic composition of the silicoflagellate and ebridian fluxes were observed between Year 1 and Year 2. The higher fluxes in Year 2 and the observed taxonomic changes imply that the upper water column in Year 2 was warmer and more eutrophic compared to Year 1, possibly linked to greater advection of nutrient-rich coastal waters to the center of the Black Sea through meso-scale eddies.
Article
A time-series particle flux study has been conducted at two sites near the Aleutian Islands: Station AB in the Bering Sea for nine years (1990–1999) and Station SA in the central subarctic Pacific for ten years (1990–2000). Significant variability in seasonal and inter-annual particle flux was observed at both stations. The annual primary flux maxima that occurred during spring through summer tended to vary considerably in their timing and magnitude, whereas the secondary maxima in fall tended to be fairly consistent of timing and flux levels. Biogenic opal contributed to a major portion of the time-series fluxes. Especially diatoms such as Neodenticula seminae are important in the biogenic opal fluxes and drive bulk of the biological system. Calcium carbonate fluxes were comprised of six species of planktonic foraminifera and mainly two species of coccolithophores. At Station AB, the fall CaCO3 flux maxima were higher than those of spring, whereas the magnitudes of the CaCO3 flux maxima were similar during both spring and fall at Station SA. The seasonal change in CaCO3 flux was significantly different from that of biogenic opal. The planktonic foraminiferal contribution was greater than that of coccoliths to the total CaCO3 flux.
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Polycystine radiolarians, phaeodarians, tintinnids, tintinnid cysts and mollluscs (chiefly pteropod protoconchae) were counted in 20 time-series sediment trap samples retrieved in the eastern equatorial Atlantic (01°47.5′N, 11°07.6′W) at 853 m, between 1 March 1989 and 16 March 1990. In addition, polycystine species were identified. Mean annual fluxes, in ind. m−2 day−1, were: polycystines: 28,446; tintinnids: 27,275; foraminifers: 17,816; tintinnid (and probably other ciliates') cysts: 14,632; phaeodarians: 1370; and molluscs: 1192. These yields are noticeably higher than most previous data from various areas of the World Ocean, which in part is attributed to the inclusion of particles <10 μm. Only 3% of the polycystines and 30% of the phaeodarians were represented by “live” cells (i.e. with protoplasm). Indirect evidence suggests that foraminifer and radiolarian fluxes probably reflect fairly well their abundances in the plankton; for the tintinnids, however, only about 0.1% of the loricae 853 m intact. With the exception of tintinnid cysts and molluscs, fluxes for the groups counted were clearly correlated with total mass and organic carbon flux and, presumably, with primary production; in the study area both peak in July-September and in January-April. It is concluded that tintinnid high reproduction rates are responsible for tightest associations between the output of their loricae and total flux. The fluxes of Foraminifera and Radiolaria, which have longer life spans (ca 1 month), are more loosely correlated with total flux, and often show peaks approximately 20–40 days after those of the latter. Molluscs, with life spans of ca 1 year, do not correlate with total flux. Juvenile Nassellaria comprised up to 44% of all polycystine shells (mean 25%). In total, 187 polycystine taxa were recorded, yet only six accounted for more than 50% of all the individuals identified. Although some species did vary in relative abundance in association with total and polycystine fluxes, these changes in assemblage composition were of very minor importance. Radiolarian equitability and the relative contribution of the Spumellaria were significantly higher at times of lower polycystine flux. These fluctuations, however, were also relatively small, and their effect woult not be expected to bias the sedimentary record toward restricted periods of higher radiolarian output. Comparison of the present data with detailed previous information for the Gulf of Alaska shows that both total radiolarian flux and its rate of accumulation throughout the year are very similar in the two areas.
Article
Sediment trap samples covering the period from September 1982 to September 1983 at Station P in the subarctic Pacific were analysed for organic carbon, nitrogen, amino acids, hexosamines and carbohydrates. One trap was deployed at 3800 m water depth for the whole period and a second trap was deployed at 1000 m from March to September 1983. Peaks of particle fluxes were observed in September–November 1982. May–June 1983 and July–September 1983. Organic compounds, used as indicators for organic matter sources and degradation, revealed that organic matter is generally least degraded during periods of maximum particle fluxes. During most of the year organic matter is derived from phytoplankton (mainly diatoms). In July to October concentrations of all measured organic compounds peak simultaneously at both trap depths, and amino acid and hexosamine fluxes are higher in the deeper trap. Spectral distributions of amino acids and hexosamines suggest that their increase is due to the addition of organic matter derived from copepods. In this case about 15% of the organic matter in the shallow trap and about 60% of the organic matter in the deep trap is contributed by copepods. The considerable enrichment of the more resistant hexosamines in the deep trap indicates that the copepods entering the traps are not active swimmers, but their decayed remains or molts.
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Sedimentary remains of fossilizable marine organisms, chiefly microplanktonic ones (coccolithophorids, silicoflagellates, diatoms, dinoflagellates, radiolarians, foraminifers) have long been used for biogeographic surveys, usually with the aim of unravelling paleoenvironmental settings. Utilization of bottom deposits (rather than plankton samples) has some advantages for this purpose: thanatocoenoses require smaller sample sizes, materials are more readily available, and they eliminate the small time-scale variability which obscures long-term trends. On the other hand, the sedimentary imprint of planktonic distributional patterns is often severely distorted by fragmentation and dissolution of the biogenic remains, reworking of sediments, winnowing and lateral advection of shells, especially toward lower latitudes, seasonally and interannually variable output rates, and the integration of vertically heterogeneous assemblages. The biases derived from these processes are reviewed, and the need for more information on selective dissolution, vertical distribution patterns and planktonic reproduction and output rates is stressed. Given the assumptions used in paleoenvironmental studies, distributional information drawn from sediment samples is less prone to yielding biased information when applied to these surveys, than to bio- or paleobiogeographic investigations; albeit the former can also be significantly affected as a result of changes in the traits that govern the formation of biogenic sediments.
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Zooplankton fecal pellets have long been thought to be a dominant component of the sedimentary flux in marine and freshwater ecosystems, but that view is changing. The last 2 decades have seen publication of >500 studies using sediment traps, which reveal that zooplankton fecal pellets often constitute only a minor or variable proportion of the sedimentary flux. Substantial proportions of this flux are from organic aggregates ('marine snow') of various origins, including phytoplankton blooms, which sediment directly to the benthos. It now appears that mainly large fecal pellets of macrozooplankton and fish are involved in the sedimentary flux. Smaller fecal pellets of microzooplankton and small mesozooplankton are mostly recycled or repackaged in the water column by microbial decomposition and coprophagy, contributing more to processes in the water column than flux to the benthos. The relative contributions of fecal pellets, marine snow and sinking phytoplankton to the vertical flux and recycling of materials in the water column are highly variable, dependent upon multiple interacting factors. These include variations in productivity, biomass, size spectra and composition of communities in the overlying water columns, and trophic interactions between various components of the plankton and nekton communities at various times, locations and depths. Other factors include differences in sinking rates, sizes, composition and pollutant contents of fecal pellets produced by various sizes of zooplankters, and zooplankton feeding-fecal pellet production interactions in relation to upwelling and El Niño periods, seasonal life-history-related zooplankton vertical migrations and long-term oceanographic regime shifts. There are also suggestions from the geological record that zooplankton fecal pellets may have been important in ancient oceans. The ecological roles of marine snow and phytoplankton aggregates in sedimentary flux also depend on a variety of interacting factors, including sources of origin, degrees of microbial colonization, depth distributions, sinking rates and ingestibility by consumers. Perhaps the major reversal of the previous paradigm on the role of fecal pellets in the sedimentary flux over the last 2 decades has been the realization that much, if not most, of the organic rain from the epipelagic to the abyss is due to direct sedimentation of aggregated phytoplankton, which does not appear to undergo consumption in the water column, and which may be related to seasonality of surface production cycles. Further, there is emerging evidence for benthic responses to sedimented phytodetritus, including apparent synchrony of reproductive cycles of some deep-sea benthic animals with seasonality of sinking of surface blooms. Such episodic input of surface phytodetritus may help resolve apparent discrepancies between average supply and demand of organic matter required to maintain benthic community metabolism. The sedimentary flux of fecal pellets, marine snow and sinking phytoplankton is an important component of the biological pump that not only transports and recycles materials in the sea but also may help scrub greenhouse gases from the atmosphere.
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Vertical distribution, gut fullness and gut contents were investigated on an aetideid copepod Gaetanus variabilis during winter at a station in the southern Japan Sea. Most individuals of C3-C6 (adult) G. variabilis were distributed between 500 and 1000 m depth. While early copepodid stages resided deeper than older ones, no diel vertical migration was detected throughout the copepodid stages. Feeding activity of G. variabilis as judged by gut fullness scores varied with developmental stage/sex, but no diel feeding rhythm was observed. Adult males cease feeding as a reflection of degeneration of their feeding appendages. The gut content analysis showed that G. variabilis is a particle feeder consuming mainly upon silicoflagellates, followed by diatoms, tintinnids and fragments of metazooplankton. An estimated daily ration of G. variabilis population based on calculated metabolic rates was 5.03 mg C m-2 day-1, which accounts for 4.5% of the local primary production or 54% of particulate organic carbon flux down to the 500 m depths at southern Japan Sea.
Article
A sediment trap array was deployed in the Southern Sohm abyssal plain, Sargasso Sea, for 75 days beginning on October 20, 1976. At the station reported in this paper, the trap collected 10. 35 g of sediment. Very large particles were rare except for a Sargassum fragment and a number of large pteropod shells. Approximately 10% of the sediment particles were larger than 62 mu m. Most of the particles were fine grained skeletal remains of plankton and clay. A small quantity of anthropogenic material was collected. Carbonate flux was approximately 18% of the total flux and consisted of 93% calcite and 7% aragonite. The flux of coccoliths was about twice that of foraminifera. The organic carbon flux was approximately 3% of the total flux and represented approximately 0. 5% of the total carbon production in this area. Pigmented particles contained in one type of fecal pellets appeared to be a major source of organic carbon transported to this depth. Fine particles such as clay and coccoliths also were transported directly from the surface layer in these fecal pellets. Refs.
Article
Modern silicoflagellate taxa found in North Pacific surface sediments are redefined and described, A new tropical species, Dictyocha calida, is introduced. Geographic distribution and relative abundance of each species are mapped for the North Pacific, based on Holocene sediment samples. The maps show that most species have definite climatic ranges, which can often be correlated with oceanic water masses. In addition, temperature preferences of certain species can be used for paleoclimatic interpretation.
Article
Siliceous dinoflagellates of the species Actiniscus pentasterias (Ehrenberg) are described from more than 20 outcrops and submarine exposures in the northeast Pacific rim area. Trends in the geographic and stratigraphic distribution of this taxon are recorded with respect to the documented abundance of the siliceous marine microflora in the interval from the Middle Miocene to the Lower Pliocene. Scanning electron micrographs of specimens illustrate the remarkable symmetry and geometry of this little-known group of microfossils.
Article
During the summer months, a layer of relatively warm surface water develops in this region, thermally stratifying the upper water column while reducing the influx of nutrients into the surface waters. The winter near-surface water is characteristically well mixed with high nutrient concentrations. Variations in the shell flux of planktonic foraminifera are considered to represent seasonality in the production of different foraminiferal species within the photic zone, and reflect changes in both phytoplankton productivity and hydrographic conditions in the upper water column. A distinct seasonal succession in the abundance of 6 planktonic foraminiferal species occurs at Station PAPA. Periods of increased foraminiferal production are due to the association of each species with one the 2 seasonal water masses, and/or to periods of high phytoplankton productivty. -from Authors
Article
Plankton and surface sediment samples from the Gulf of California were examined to determine the present geographic distribution of silicoflagellate species in this area. Variations in the species composition of the silicoflagellate assemblage were found to be related to water mass distributions. Eight species were identified in these samples. Octactis pulchra is associated with high levels of primary productivity in the surface waters and is found in greatest abundance in the central Gulf of California. Dictyocha messanensis dominates the silicoflagellate assemblage in stations outside the Gulf of California and increases in relative abundance with decreasing amounts of Octactis pulchra. Dictyocha calida, Dictyocha sp. A, and Dictyocha sp. B are associated with equatorial waters and have the highest relative abundance near the mouth of the Gulf. Dictyocha epiodon and Distephanus speculum are associated with cold California Current Water, and Dictyocha epiodon is present in minor abundance in Gulf samples. Dictyocha sp. 2 has a patchy distribution with low relative abundance.
Three assemblages of Quaternary siliceous microfossils were dissolved for varying lengths of time in natural seawater. Changes in the relative abundances of certain radiolarians, diatoms, and sponge spicules were measured, and a dissolution index scheme was developed. This scheme allows an objective assessment of the preservation of tropical siliceous microfossil assemblages of Quaternary age. Its application to a study of near-surface sediments in the eastern tropical Pacific shows that the siliceous microfossil preservation pattern roughly reflects surface water productivity. Two second-order features are superimposed upon this pattern. First, preservation is usually better at deeper depositional sites at most latitudes, and this is attributed primarily to sediment redistribution processes. Second, the best preservation is found not in equatorial sediments, but in those obtained from an area near 10°N, 117°W. This is attributed to the unusually high abundance of fragments of the diatom genus Ethmodiscus found in those sediments.
Article
Oceanic waters of the subarctic Pacific exhibit a special ecological feature, a virtually seasonally invariant standing stock of phytoplankton (measured as chlorophyll a), that seems to reflect a balance, at least during spring and summer, between phytoplankton growth and zooplankton grazing. The grazers presumed to be responsible for the balance are the calanoid copepodsNeocalanus cristatus andN. plumchrus. Shipboard grazing experiments, utilizing both natural suspended particulate material and cultured phytoplankton as food for the copepods, showed that both species have at least three attributes of feeding behavior required to maintain steady standing stock of phytoplankton. That is, theNeocalanus species can feed at the low concentrations of phytoplankton that prevail in the open subarctic Pacific, they feed at similar rates on a broad range of particlessizes including the predominant particles, and they respond to small increases in phytoplankton concentration by proportionately larger increases in their feeding rate. Although both species ofNeocalanus attain larger body sizes than co-occurringCalanus pacificus andPseudocalanus sp., they have morphological specializations that seem to account for their unexpected ability to feed on very dilute suspensions of small phytoplankton cells. It appears that the perpetually low phytoplankton concentrations in the open subarctic Pacific do not permit maximum feeding effort by the species ofNeocalanus.
A description and numerical analysis of the factors affecting the processes of production in the Gulf of Alaska
  • G C Anderson
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  • B C Booth
  • J M Glass
Anderson, G. C., R. K. Lam, B. C. Booth and J. M. Glass. 1977. A description and numerical analysis of the factors affecting the processes of production in the Gulf of Alaska. Univ. of
Interannual time series sediment trap experiment at Ocean Station Papa, North Pacific
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Honjo, S. and C. S. Wong. 1985, abstract. Interannual time series sediment trap experiment at Ocean Station Papa, North Pacific. EOS, 66, 1282.
Material flux at weather station PAPA, high frequency time series observations through production cycles. EOS, 65. 225
  • C S Wong
  • S Honjo
Wong, C. S. and S. Honjo. 1984, abstract. Material flux at weather station PAPA, high frequency time series observations through production cycles. EOS, 65. 225. Received: 2 June, 1986; revised: 23 March, I98Z
Statistics and Data Analysis in Geology Cenozoic endoskeletal dinoflagellates in southwestern Pacific sediments cored during Leg 21 ofthe DSDP, in Initial Reports Deep Sea Drilling Project
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Davis, J. C. 1973. Statistics and Data Analysis in Geology. John Wiley & Sons, NY, 550 pp. Dumitrica, P. 1973. Cenozoic endoskeletal dinoflagellates in southwestern Pacific sediments cored during Leg 21 ofthe DSDP, in Initial Reports Deep Sea Drilling Project, J. E. Andrews et al., eds., U.S. Government Printing OMce, Washington, DC, 21, 819-884.
1985, abstract. In-situ preservation of biogenic material collected by a deep ocean sediment trap
  • S J Manganini
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Manganini, S. J. and S. Honjo. 1985, abstract. In-situ preservation of biogenic material collected by a deep ocean sediment trap. EOS, 66, 1292.
Sedimentation of materials in the Sargasso Sea at a 5,367 m deep station Study of ocean fluxes in time and space by bottom-tethered sediment trap arrays: a recommendation
  • S Honjo
Honjo, S. 1978. Sedimentation of materials in the Sargasso Sea at a 5,367 m deep station. J, Mar. Res., 36, 469-492. 1984. Study of ocean fluxes in time and space by bottom-tethered sediment trap arrays: a recommendation. Global Ocean Flux Study Workshop, National Research Council, Washington, DC, 304-324.
0ceanographic observations at Ocean Station P. Pacific Marine Science Report Series, volumes 1 to 125
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Anonymous. 1981. 0ceanographic observations at Ocean Station P. Pacific Marine Science Report Series, volumes 1 to 125. Institute of Ocean Sciences, Patricia Bay, Sidney, B.C., Canada.
Variaciones de Dictyocha .fibula en el Golfo de San Matias (Patagonia septentrional): An. Mus. Argentina Cienc. Nat
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Frenguelli, J. 1935. Variaciones de Dictyocha.fibula en el Golfo de San Matias (Patagonia septentrional): An. Mus. Argentina Cienc. Nat. "Bernadino Rivadavia," v. 38, Protistol. No. 4, 265-281. Journal of Marine Research [4 5, 2
Statistics of oceanographic data based on hydrographic/STD casts made at Ocean Station P during
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Tabata, S. and J. L. Peart. 1985. Statistics of oceanographic data based on hydrographic/STD casts made at Ocean Station P during August 1956 through June 1981. Canadian Data Report of Hydrography and Ocean Sciences, No. 31.
Silicoflagellate remains in the sediments of Lake Hiruga
  • M Shitanaka
Shitanaka, M. 1983. Silicoflagellate remains in the sediments of Lake Hiruga, Fukui, Japan. Mizunami fossil Museum Research Report, v. 10, 171-180 (in Japanese).
Cenozoic endoskeletal dinoflagellates in southwestern Pacific sediments cored during Leg 21 ofthe DSDP, in Initial Reports Deep Sea Drilling Project
  • P Dumitrica
Dumitrica, P. 1973. Cenozoic endoskeletal dinoflagellates in southwestern Pacific sediments cored during Leg 21 ofthe DSDP, in Initial Reports Deep Sea Drilling Project, J. E. Andrews et al., eds., U.S. Government Printing OMce, Washington, DC, 21, 819-884.
Two year time•-series fluxes of silicoflagellates and Actiniscus: size fractioned results from subarctic Pacific Station PAPA, 1982-1984
  • K Takahashi
Takahashi, K. 1983. Radiolarian biocoenosis-thanatocoenosis relationship in pelagic oceans. Amer. Assoc. Petrol. Geol. Bull., 67, 556-557. 1985. Two year time•-series fluxes of silicoflagellates and Actiniscus: size fractioned results from subarctic Pacific Station PAPA, 1982-1984. Woods Hole Oceanographic Institution Technical Report, WHOI-85-41. 1986. Seasonal fluxes of pelagic diatoms in the subarctic Pacific, 1982-1983. Deep-Sea Res., 33, 1225-1251.
Silicoflagellates and Actiniscus: vertical fluxes at Pacific and Atlantic sediment trap stations
1987a. Silicoflagellates and Actiniscus: vertical fluxes at Pacific and Atlantic sediment trap stations, in Ocean Biocoenosis, S. Honjo, ed., Micropaleontology Press, NY. I987b. Response of subarctic Pacific diatom fluxes to 1982-1983 El Nifio. J. Geophys. Res., (submitted).