Anoxic Cariaco Basin Research Articles

Diverse secondary metabolites are expressed in particle-associated and free-living microorganisms of the permanently anoxic Cariaco Basin

Secondary metabolites play essential roles in ecological interactions and nutrient acquisition, and are of interest for their potential uses in medicine and biotechnology. Genome mining for biosynthetic gene clusters (BGCs) can be used for the discovery of new compounds. Here, we use metagenomics and metatranscriptomics to analyze BGCs in free-living and particle-associated microbial communities through the stratified water column of the Cariaco Basin, Venezuela. We recovered 565 bacterial and archaeal metagenome-assembled genomes (MAGs) and identified 1154 diverse BGCs. We show that differences in water redox potential and microbial lifestyle (particle-associated vs. free-living) are associated with variations in the predicted composition and production of secondary metabolites. Our results indicate that microbes, including understudied clades such as Planctomycetota, potentially produce a wide range of secondary metabolites in these anoxic/euxinic waters.

Transport-limited reactions in microbial systems.

Predicting microbial metabolic rates and emergent biogeochemical fluxes remains challenging due to the many unknown population dynamical, physiological and reaction-kinetic parameters and uncertainties in species composition. Here, we show that the need for these parameters can be eliminated when population dynamics and reaction kinetics operate at much shorter time scales than physical mixing processes. Such scenarios are widespread in poorly mixed water columns and sediments. In this 'fast-reaction-transport' (FRT) limit, all that is required for predictions are chemical boundary conditions, the physical mixing processes and reaction stoichiometries, while no knowledge of species composition, physiology or population/reaction kinetic parameters is needed. Using time-series data spanning years 2001-2014 and depths 180-900 m across the permanently anoxic Cariaco Basin, we demonstrate that the FRT approach can accurately predict the dynamics of major electron donors and acceptors (Pearson r ≥ 0.9 in all cases). Hence, many microbial processes in this system are largely transport limited and thus predictable regardless of species composition, population dynamics and kinetics. Our approach enables predictions for many systems in which microbial community dynamics and kinetics are unknown. Our findings also reveal a mechanism for the frequently observed decoupling between function and taxonomy in microbial systems.

Eukaryotic Parasites Are Integral to a Productive Microbial Food Web in Oxygen-Depleted Waters.

Oxygen-depleted water columns (ODWCs) host a diverse community of eukaryotic protists that change dramatically in composition over the oxic-anoxic gradient. In the permanently anoxic Cariaco Basin, peaks in eukaryotic diversity occurred in layers where dark microbial activity (chemoautotrophy and heterotrophy) were highest, suggesting a link between prokaryotic activity and trophic associations with protists. Using 18S rRNA gene sequencing, parasites and especially the obligate parasitic clade, Syndiniales, appear to be particularly abundant, suggesting parasitism is an important, but overlooked interaction in ODWC food webs. Syndiniales were also associated with certain prokaryotic groups that are often found in ODWCs, including Marinimicrobia and Marine Group II archaea, evocative of feedbacks between parasitic infection events, release of organic matter, and prokaryotic assimilative activity. In a network analysis that included all three domains of life, bacterial and archaeal taxa were putative bottleneck and hub species, while a large proportion of edges were connected to eukaryotic nodes. Inclusion of parasites resulted in a more complex network with longer path lengths between members. Together, these results suggest that protists, and especially protistan parasites, play an important role in maintaining microbial food web complexity, particularly in ODWCs, where protist diversity and microbial productivity are high, but energy resources are limited relative to euphotic waters.

Environmental determinants of the distribution of planktonic diplonemids and kinetoplastids in the oceans.

We analysed a widely used barcode, the V9 region of the 18S rRNA gene, to study the effect of environmental conditions on the distribution of two related heterotrophic protistan lineages in marine plankton, kinetoplastids and diplonemids. We relied on a major published dataset (Tara Oceans) where samples from the mesopelagic zone were available from just 32 of 123 locations, and both groups are most abundant in this zone. To close sampling gaps and obtain more information from the deeper ocean, we collected 57 new samples targeting especially the mesopelagic zone. We sampled in three geographic regions: the Arctic, two depth transects in the Adriatic Sea, and the anoxic Cariaco Basin. In agreement with previous studies, both protist groups are most abundant and diverse in the mesopelagic zone. In addition to that, we found that their abundance, richness, and community structure also depend on geography, oxygen concentration, salinity, temperature, and other environmental variables reflecting the abundance of algae and nutrients. Both groups studied here demonstrated similar patterns, although some differences were also observed. Kinetoplastids and diplonemids prefer tropical regions and nutrient-rich conditions and avoid high oxygen concentration, high salinity, and high density of algae.

Total dissolved atmospheric nitrogen deposition in the anoxic Cariaco basin

Atmospheric deposition of total dissolved nitrogen (TDN) is an important source of nitrogen for ocean primary productivity that has increased since the industrial revolution. Thus, understanding its role in the ocean nitrogen cycle will help assess recent changes in ocean biogeochemistry. In the anoxic Cariaco basin, the place of the CARIACO Ocean Time-Series Program, the influence of atmospherically-deposited TDN on marine biogeochemistry is unknown. In this study, we measured atmospheric TDN concentrations as dissolved organic (DON) and inorganic (DIN) nitrogen (TDN = DIN + DON) in atmospheric suspended particles and wet deposition samples at the northeast of the basin during periods of the wet (August–September 2008) and dry (March–April 2009) seasons. We evaluated the potential anthropogenic N influences by measuring wind velocity and direction, size-fractionated suspended particles, chemical traces and by performing back trajectories. We found DIN and DON concentration values that ranged between 0.11 and 0.58 μg-N m−3 and 0.11–0.56 μg-N m−3 in total suspended particles samples and between 0.08 and 0.54 mg-N l−1 and 0.02–1.3 mg-N l−1 in wet deposition samples, respectively. Continental air masses increased DON and DIN concentrations in atmospheric suspended particles during the wet season. We estimate an annual TDN atmospheric deposition (wet + particles) of 3.6 × 103 ton-N year−1 and concluded that: 1) Atmospheric supply of TDN plays a key role in the C and N budget of the basin because replaces a fraction of the C (20% by induced primary production) and N (40%) removed by sediment burial, 2) present anthropogenic N could contribute to 30% of TDN atmospheric deposition in the basin, and 3) reduced DON (gas + particles) should be a significant component of bulk N deposition.

Free-living chemoautotrophic and particle-attached heterotrophic prokaryotes dominate microbial assemblages along a pelagic redox gradient.

Using the anoxic Cariaco Basin as a natural laboratory, particle association of bacterial and archaeal taxa was assessed by iTag sequencing and qPCR gene assays of samples spanning an oxic-anoxic-euxinic gradient. A total of 10%-12% of all bacterial and archaeal cells were found in the particle-associated (PA) fraction, operationally defined as prokaryotes captured on 2.7µm membranes. Both redox condition and size fraction segregated bacterial taxa. Archaeal taxa varied according to redox conditions, but were similar between size fractions. Taxa putatively associated with chemoautotrophic sulfur oxidation and nitrification dominated the free-living (FL) fraction throughout the oxycline (<1-120µM O2 ) and upper anoxic layer. Bacteria in the oxycline's PA fraction included taxa known to be aerobic and anaerobic chemoorganotrophs. At shallow anoxic depths, PA taxa were primarily affiliated with anaerobic sulfate ( SO42-)-reducing lineages. PA fractions in the most sulfidic samples were dominated by taxa affiliated with CH4 oxidizing, fermenting and SO42- reducing lineages. Prevalence of particle-associated SO42--reducing taxa and abundant sulfur-oxidizing taxa in both size fractions across the oxic-anoxic interface is consistent with the cryptic sulfur cycling concept. Bacterial assemblage diversity in the PA fraction always exceeded the FL fraction except in the most oxic samples, whereas Archaeal diversity was not consistently different between size fractions. Our results suggest that these particle-associated and free-living bacterial assemblages are functionally different and that the interplay between particle microhabitats and surrounding geochemical regimes is a strong selective force shaping microbial communities throughout the water column.

Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments

Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are 34S-enriched relative to coexisting sulfide, and experiments have produced 34S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography – inductively coupled plasma mass spectrometry, to measure the compound-specific sulfur isotopic compositions of volatile organosulfur compounds over a 6m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in 34S relative to coexisting kerogen and porewater sulfide. We hypothesize that this 34S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon–sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary porewater. The 34S-depleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.

Sea change: Charting the course for biogeochemical ocean time-series research in a new millennium

Ocean time-series provide vital information needed for assessing ecosystem change. This paper summarizes the historical context, major program objectives, and future research priorities for three contemporary ocean time-series programs: The Hawaii Ocean Time-series (HOT), the Bermuda Atlantic Time-series Study (BATS), and the CARIACO Ocean Time-Series. These three programs operate in physically and biogeochemically distinct regions of the world's oceans, with HOT and BATS located in the open-ocean waters of the subtropical North Pacific and North Atlantic, respectively, and CARIACO situated in the anoxic Cariaco Basin of the tropical Atlantic. All three programs sustain near-monthly shipboard occupations of their field sampling sites, with HOT and BATS beginning in 1988, and CARIACO initiated in 1996. The resulting data provide some of the only multi-disciplinary, decadal-scale determinations of time-varying ecosystem change in the global ocean. Facilitated by a scoping workshop (September 2010) sponsored by the Ocean Carbon Biogeochemistry (OCB) program, leaders of these time-series programs sought community input on existing program strengths and for future research directions. Themes that emerged from these discussions included:1. Shipboard time-series programs are key to informing our understanding of the connectivity between changes in ocean-climate and biogeochemistry.2. The scientific and logistical support provided by shipboard time-series programs forms the backbone for numerous research and education programs. Future studies should be encouraged that seek mechanistic understanding of ecological interactions underlying the biogeochemical dynamics at these sites.3. Detecting time-varying trends in ocean properties and processes requires consistent, high-quality measurements. Time-series must carefully document analytical procedures and, where possible, trace the accuracy of analyses to certified standards and internal reference materials.4. Leveraged implementation, testing, and validation of autonomous and remote observing technologies at time-series sites provide new insights into spatiotemporal variability underlying ecosystem changes.5. The value of existing time-series data for formulating and validating ecosystem models should be promoted.In summary, the scientific underpinnings of ocean time-series programs remain as strong and important today as when these programs were initiated. The emerging data inform our knowledge of the ocean's biogeochemistry and ecology, and improve our predictive capacity about planetary change.

Class Cariacotrichea, a novel ciliate taxon from the anoxic Cariaco Basin, Venezuela

The majority of environmental micro-organisms identified with the rRNA approach have never been visualized. Thus, their reliable classification and taxonomic assignment is often difficult or even impossible. In our preliminary 18S rRNA gene sequencing work from the world's largest anoxic marine environment, the Cariaco Basin (Caribbean Sea, Venezuela), we detected a ciliate clade, designated previously as CAR_H [Stoeck, S., Taylor, G. T. & Epstein, S. S. (2003). Appl Environ Microbiol 63, 5656-5663]. Here, we combine the traditional rRNA detection method of fluorescent in situ hybridization (FISH) with scanning electron microscopy (SEM) and confirm the phylogenetic separation of the CAR_H sequences from all other ciliate classes by showing an outstanding morphological feature of this group: a unique, archway-shaped kinety surrounding the oral apparatus and extending to the posterior body end in CAR_H cells. Based on this specific feature and the molecular phylogenies, we propose a novel ciliate class, Cariacotrichea nov. cl.

Accessing marine protists from the anoxic Cariaco Basin

The earliest microbial cells evolved in an anoxic ocean (Martin and Muller, 1998), and many argue that the earliest Eukarya arose in the absence of oxygen as well. The microbe-mediated biogeochemical processes taking place below oxic/anoxic interfaces are of undeniable importance and interest, and the Cariaco Basin off the coast of Venezuela is a superb model ecosystem in this regard. It is the world’s largest body of truly marine anoxic waters and has been almost continuously anoxic for at least the last 2M years (Schubert, 1982). Consequently, the Basin became the site of many investigations, including a long-term biogeochemical time series initiated in 1995 (Muller-Karger et al., 2001; Taylor et al., 2001) and an NSF-funded Microbial Observatory established in 2004. This Observatory was a multi-year, multi-investigator international effort. Its principal goals were: to combine molecular and cell-based approaches to survey microbial Eukarya among geochemically diverse habitats in the Basin; to analyze the community structure and its dynamics across time and space; to discover novel organisms, and to gain insights into what governs their distribution dispersal and biogeography.

Hydrolytic ectoenzyme activity associated with suspended and sinking organic particles within the anoxic Cariaco Basin

Ectohydrolase activities of suspended microbiota were compared to those associated with sinking particles (sed-POM) retrieved from sediment traps deployed in the permanently anoxic Cariaco Basin. In shore-based assays, activities of aminopeptidase, β-glucosidase, chitinase and alkaline phosphatase were measured in samples obtained from oxic and anoxic depths using MUF- and MCA-labeled fluorogenic substrate analogs. Hydrolysis potentials for these enzymes in the seston varied widely over the nine cruises sampled (8 Nov 1996–3 May 2000) and among depths (15–1265 m); from <10 to over 1600 nM d −1 hydrolysate released, generally co-varying with one another and with suspended particulate organic carbon (POC) and particulate nitrogen (PN). Hydrolytic potentials, prokaryotic abundances and POC/PN concentrations in sinking debris were 400–1.3×10 7 times higher than in comparable volumes of seawater. However when normalized to PN, hydrolytic potentials in sediment trap samples were not demonstrably higher than in Niskin bottle samples. We estimate that PN pools in sediment trap samples were turned over 2–1400 times (medians=7–26 x) slower by hydrolysis than were suspended PN pools. Median prokaryotic growth rates (divisions d −1) in sinking debris were also ∼150 times slower than for bacterioplankton. Hydrolytic potentials in surface oxic waters were generally faster than in underlying anoxic waters on a volumetric basis (nM hydrolysate d −1), but were not significantly ( p>0.05) different when normalized to PN or prokaryote abundances. Alkaline phosphatase was consistently the most active ectohydrolase in both sample types, suggesting that Cariaco Basin assemblages were adapted to decomposing phosphate esters in organic polymers. However, phosphorus limitation was not evident from nutrient inventories in the water column. Results support the hypothesis that efficiencies of polymer hydrolysis in anoxic waters are not inherently lower than in oxic waters.

Si cycle in the Cariaco Basin, Venezuela: Seasonal variability in silicate availability and the Si:C:N composition of sinking particles

A 9‐year time series of water column and sediment trap measurements was used to examine silicon cycling within the anoxic Cariaco Basin. The dynamic hydrographic regime within Cariaco Basin results in strong seasonal changes in nutrient availability and the Si:C:N of sinking particles. Upwelling in early winter injects silicic acid (Si(OH)4= ) and nitrate (NO3−) rich waters into the photic zone which stimulates primary production and results in opal fluxes in excess of 4 mmol Si m−2 d−1. However, even during upwelling, surface waters tend to be depleted (&lt;1 μM) in both Si(OH)4= and NO3− as a result of rapid utilization. In most years, the upper water column during winter and spring is marked by Si(OH)4= :NO3− and Si* values of less than 1. This indicates that silicate limitation in Cariaco Basin is most severe during upwelling and may restrict diatom production. Conversely, during the summer and fall when upwelling is reduced, Si(OH)4= :NO3− ratios in the upper 50 m of the water column exceed 10, implying that nitrate rather than silicate is acting to limit production during this time of year. On average, sinking particles collected at 150‐m depth in the Cariaco Basin have Si:C and Si:N values of 0.17 ± 0.01 and 1.14 ± 0.10, respectively. These ratios increase with depth to 400 m and then remain relatively constant, suggesting minimal selective removal of elements with remineralization in the anoxic portion of the water column. Similar depth‐dependent changes in these ratios are seen in surface sediments from the basin. Seasonally, particulate Si:C and Si:N are highest during the early part of the year when upwelling is most intense, while both ratios decrease to their lowest values during summer and fall. The observed seasonal variability in these ratios is due to changes in both nutrient utilization by diatoms and the contribution of diatoms to the total phytoplankton. The high ratios during upwelling suggest enhanced export of Si relative to C and N during this time of year.

Neotropical vegetation response to rapid climate changes during the last glacial period: Palynological evidence from the Cariaco Basin

We present new palynological information from the anoxic Cariaco Basin, off Venezuela, that provides insight into the response of northernmost South American vegetation to rapid climate changes between 68 and 28 ka, specifically during North Atlantic Heinrich events (HEs) and Dansgaard/Oeschger cycles. We defined three different vegetation modes: (1) an interstadial mode characterized by the highest pollen concentration and the maximum extension of semi-deciduous and evergreen forests; (2) a stadial mode characterized by increases of salt marshes, herbs, and montane forests; and (3) a Heinrich event mode characterized by the lowest pollen concentrations, abrupt increases of salt marshes, and decreased forest abundance. Similarly, indices of C4/C3 plants show increases during stadials with clear peaks during the onset of HEs, though grasslands did not become dominant during these periods. We alternatively propose that these expansions of C4 plants are associated with the expansion of coastal salt marshes. Our vegetation record suggests the prevalence of humid conditions during interstadials, dry and cold conditions during stadials, and dry and cold conditions together with changes in sea level during HEs. This new palynological evidence supports previous interpretations that main environmental changes in northernmost South America were driven by latitudinal displacements of the Intertropical Convergence Zone and sea-level changes.

Spatiotemporal dynamics of bacterial populations in the anoxic Cariaco Basin

Distributions of bacterial populations in the anoxic Cariaco Basin were studied over 2 yr (five cruises) at three stations using fluorescence in situ hybridization (FISH) and terminal restriction fragment length polymorphism (T‐RFLP) of 16S ribosomal ribonucleic acid (rRNA) genes. FISH results demonstrate that the contribution of ɛ‐proteobacterial abundances to total prokaryotic inventories was relatively constant among cruises, and this group was dominant in the redoxcline, accounting for 18% of DAPI (4'6‐diamidino‐2‐phenylindole)‐stained counts on average. In contrast, β‐proteobacteria were more variable. Sulfate reducers, α‐, and γ‐proteobacteria accounted for minor components of the anaerobic microbial communities. T‐RFLP fingerprinting also showed significant temporal shifts in bacterial community composition. The greatest variations in bacterial community structure were evident among oxic, transitional, and anoxic zones, but significant horizontal variations were also evident within redoxclines of three different stations. A statistical analysis of T‐RFLP patterns revealed clear spatiotemporal patterns in bacterial community structure along the redox gradient among sites and over time. Total prokaryotic abundances corresponded well with seasonal variations in organic carbon fluxes above the redoxcline. However, no single measured environmental variable (O2, H2S, S2O32‐, H4SiO4, NO3−, PO43‐, microbial biomass, chemoautotrophic production) explained the temporal oscillations of the dominant bacterial groups. Analyses suggest that redox gradients, terrestrial inputs, and disturbance due to lateral intrusions of adjacent waters could significantly affect bacterial community composition in the Cariaco Basin.

Compositional responses of bacterial communities to redox gradients and grazing in the anoxic Cariaco Basin

During a May 2005 cruise, depth-dependent distributions of bacterial populations and their responses to predator exclusion were investigated in the anoxic Cariaco Basin, Venezuela. Community structure was assessed using fluorescence in situ hybridization (FISH) and terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes. FISH combined with microautoradiography was used to determine single-cell activity of heterotrophic bacterial popula- tions provided with 3 H-leucine substrate. FISH and T-RFLP patterns clearly illustrated shifts in bac- terial community composition as waters transitioned from oxic to anoxic conditions at depth. Preda- tor-exclusion experiments were conducted at 3 depths across the redoxcline. Although richness of bacterial operational taxonomic units (OTUs) was initially reduced at all 3 depths (250, 270, 400 m) as a likely consequence of confinement, distinct responses of individual OTUs to predator exclusion were detected in T-RFLP patterns. FISH analyses also detected very consistent responses of α-, β-, γ-, and e-proteobacteria to predator exclusion. The α- and β-proteobacteria became more prevalent in controls than in 'predator-free' samples (<1.6 µm filtrate) over time. In contrast, γ- and e-proteobacte- ria gained prevalence in 'predator-free' samples. Interestingly, abundances of β-proteobacteria dra- matically declined over time in both controls and predator-free treatments, and none actively assim- ilated 3 H-leucine (MICRO-FISH). Among 3 H-leucine-assimilating cells in control samples at 270 m, α-, γ-, and e-proteobacteria accounted for 12, 38, and 14% of 3 H-leucine active cells, respectively. Taxonomic distributions of 3 H-leucine-assimilating cells in predator-exclusion treatments did not detectably differ from controls. Overall, results demonstrated that redox gradients structured microbial communities and that predator exclusion significantly altered bacterial abundances and community composition.

Comparison of Vertical Distributions of Prokaryotic Assemblages in the Anoxic Cariaco Basin and Black Sea by Use of Fluorescence In Situ Hybridization

Individual prokaryotic cells from two major anoxic basins, the Cariaco Basin and the Black Sea, were enumerated throughout their water columns using fluorescence in situ hybridization (FISH) with the fluorochrome Cy3 or horseradish peroxidase-modified oligonucleotide probes. For both basins, significant differences in total prokaryotic abundance and phylogenetic composition were observed among oxic, anoxic, and transitional (redoxcline) waters. Epsilon-proteobacteria, Crenarchaeota, and Euryarchaeota were more prevalent in the redoxclines, where previous studies reported high rates of chemoautotrophic production relative to those in waters above and below the redoxclines. Relative abundances of Archaea in both systems varied between 1% and 28% of total prokaryotes, depending on depth. The prokaryotic community composition varied between the two anoxic basins, consistent with distinct geochemical and physical conditions. In the Black Sea, the relative contributions of group I Crenarchaeota (median, 5.5%) to prokaryotic communities were significantly higher (P < 0.001; n = 20) than those of group II Euryarchaeota (median, 2.9%). In contrast, their proportions were nearly equivalent in the Cariaco Basin. Beta-proteobacteria were unexpectedly common throughout the Cariaco Basin's water column, accounting for an average of 47% of 4',6'-diamidino-2-phenylindole (DAPI)-stained cells. This group was below the detection limit (<1%) in the Black Sea samples. Compositional differences between basins may reflect temporal variability in microbial populations and/or systematic differences in environmental conditions and the populations for which they select.

Novel eukaryotes from the permanently anoxic Cariaco Basin (Caribbean Sea).

Present knowledge of microbial diversity is decidedly incomplete (S. J. Giovannoni and M. S. Rappé, p. 47-84, in D. Kirchman, ed., Microbial Ecology of the Oceans, 2000; E. Stackebrandt and T. M. Embley, p. 57-75, in R. R. Colwell and D. J. Grimes, ed., Nonculturable Microorganisms in the Environment, 2000). Protistan phylogenies are particularly deficient and undoubtedly exclude clades of principal ecological and evolutionary importance (S. L. Baldauf, Science 300:1703-1706, 2003). The rRNA approach has been extraordinarily successful in expanding the global prokaryotic record (S. J. Giovannoni and M. S. Rappé, p. 47-84, in D. Kirchman, ed., Microbial Ecology of the Oceans, 2000; E. Stackebrandt and T. M. Embley, p. 57-75, in R. R. Colwell and D. J. Grimes, ed., Nonculturable Microorganisms in the Environment, 2000) but has rarely been used in protistan discovery. Here we report the first application of the 18S rRNA approach to a permanently anoxic environment, the Cariaco Basin off the Venezuelan coast. On the basis of rRNA sequences, we uncovered a substantial number of novel protistan lineages. These included new clades of the highest taxonomic level unrelated to any known eukaryote as well as deep branches within established protistan groups. Three novel lineages branch at the base of the eukaryotic evolutionary tree preceding, contemporary with, or immediately following the earliest eukaryotic branches. These newly discovered protists may retain traits reminiscent of an early eukaryotic ancestor(s).

Climate and the collapse of Maya civilization.

In the anoxic Cariaco Basin of the southern Caribbean, the bulk titanium content of undisturbed sediment reflects variations in riverine input and the hydrological cycle over northern tropical South America. A seasonally resolved record of titanium shows that the collapse of Maya civilization in the Terminal Classic Period occurred during an extended regional dry period, punctuated by more intense multiyear droughts centered at approximately 810, 860, and 910 A.D. These new data suggest that a century-scale decline in rainfall put a general strain on resources in the region, which was then exacerbated by abrupt drought events, contributing to the social stresses that led to the Maya demise.

Temporal variations in viral distributions in the anoxic Cariaco Basin

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 30:103-116 (2003) - doi:10.3354/ame030103 Temporal variations in viral distributions in the anoxic Cariaco Basin G. T. Taylor*, C. Hein, M. Iabichella Marine Sciences Research Center, Stony Brook University, Stony Brook, New York 11794-5000, USA *Email: gtaylor@notes.cc.sunysb.edu ABSTRACT: Virus-like particles (VLP), collected from the permanently anoxic Cariaco Basin between 10 October 1996 and 2 November 1999, were enumerated in water column and sediment trap samples. Vertical distributions of VLP from 18 depths between 7 and 1310 m generally corresponded to those of bacterial abundance and bacterial net production (BNP), with primary maxima consistently found in surface waters and midwater maxima near the O2/H2S interface. Temporal variations in VLP concentrations (0.81 to 630 x 108 VLP l-1) were highly correlated with chlorophyll a (chl a), bacterial abundance and BNP in the upper 250 m. In the redox transition zone (RTZ = 250 to 450 m), VLP abundance covaried with bacterial growth rates, but not bacterial abundance nor chemoautotrophic production. In the anoxic layer (>450 m), temporal variations in VLP abundance were not significantly correlated with any measured variable. In the RTZ, the median VLP:bacteria ratio (VBR = 3) was significantly lower than in the oxic (VBR = 16) and anoxic (VBR = 31) layers for all observations, suggesting varying relationships between viruses, hosts and environment among these layers. Vertical fluxes of VLP associated with sedimenting debris varied between 0.39 and 520 x 109 VLP m-2 d-1, a range similar to bacteria (0.88 to 330 x 109 bacteria m-2 d-1). VBRs in the sinking inventories were very low, varying from 0.01 to 1.2 and averaging 0.60, suggesting that VLP are not as numerically important in sinking particles as they are in suspended communities. Comparisons of sinking fluxes with suspended VLP inventories indicate that vertical transport is relatively unimportant in redistributing viruses in the water column. Estimated removal rates by sinking from the oxic, transition and anoxic layers averaged 0.11% mo-1 (n = 16) for apparent VLP. KEY WORDS: Viruses · Bacteria · Anoxia · Bacterial production · Microbial loop · Cariaco Basin Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 30, No. 2. Online publication date: January 07, 2003 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2003 Inter-Research.

Southward migration of the intertropical convergence zone through the Holocene.

Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene "thermal maximum." Since approximately 5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the "Little Ice Age." These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.