Showing papers by "Woods Hole Oceanographic Institution published in 1995"

Phylogenetic relationships of Thiomicrospira species and their identification in deep-sea hydrothermal vent samples by denaturing gradient gel electrophoresis of 16S rDNA fragments

Abstract: Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA fragments was used to explore the genetic diversity of hydrothermal vent microbial communities, specifically to determine the importance of sulfur-oxidizing bacteria therein. DGGE analysis of two different hydrothermal vent samples revealed one PCR band for one sample and three PCR bands for the other sample, which probably correspond to the dominant bacterial populations in these communities. Three of the four 16S rDNA fragments were sequenced. By comparison with 16S rRNA sequences of the Ribosomal Database Project, two of the DGGE-separated fragments were assigned to the genus Thiomicrospira. To identify these 'phylotypes' in more detail, a phylogenetic framework was created by determining the nearly complete 16S rRNA gene sequence (approx. 1500 nucleotides) from three described Thiomicrospira species, viz., Tms. crunogena, Tms. pelophila, Tms. denitrificans, and from a new isolate, Thiomicrospira sp. strain MA2-6. All Thiomicrospira species except Tms. denitrificans formed a monophyletic group within the gamma subdivision of the Proteobacteria. Tms. denitrificans was assigned as a member of the epsilon subdivision and was distantly affiliated with Thiovulum, another sulfur-oxidizing bacterium. Sequences of two dominant 16S rDNA fragments obtained by DGGE analysis fell into the gamma subdivision Thiomicrospira. The sequence of one fragment was in all comparable positions identical to the 16S rRNA sequence of Tms. crunogena. Identifying a dominant molecular isolate as Tms. crunogena indicates that this species is a dominant community member of hydrothermal vent sites. Another 'phylotype' represented a new Thiomicrospira species, phylogenetically in an intermediate position between Tms. crunogena and Tms. pelophila. The third 'phylotype' was identified as a Desulfovibrio, indicating that sulfate-reducing bacteria, as sources of sulfide, may complement sulfur- and sulfide-oxidizing bacteria ecologically in these sulfide-producing hydrothermal vents.

Extraction of mid-ocean-ridge basalt from the upwelling mantle by focused flow of melt in dunite channels

Abstract: Like residual peridotites from mid-ocean ridges, peridotites from the mantle section of the Oman ophiolite are far from equilibrium with mid-ocean-ridge basalt (MORB). By contrast, dunites from Oman are close to equilibrium with MORB, indicating that they were conduits for focused melt flow. Formation of dunite conduits by porous flow is sufficient to explain extraction of MORB from the mantle, and fracture mechanisms may not be necessary in this process.

Genesis of high Mg# andesites and the continental crust

Abstract: The continental crust has an andesitic composition with high Mg/(Mg+Fe) and Ni contents which may be too high to have formed by differentiation of basaltic magmas. Instead, mantle-derived, high Mg# andesites (HMA) may form a substantial component of the crust. HMA may be produced by partial melting of previously depleted, subsequently metasomatised mantle peridotite. However, they are more likely produced by reaction between ascending melts and mantle peridotite. HMA are less common than basalts among lavas in modern island arcs, but may have been more common in the past, may be produced in specific environments (such as “ridge subduction”), may be more common among plutonic rocks in the lower and middle crust than among lavas at the surface, and may be selectively preserved during later erosion and subduction processes.

The Aquatic Chemistry of Rare Earth Elements in Rivers and Estuaries

Abstract: Laboratory experiments were carried out to determine how pH, colloids and salinity control the fractionation of rare earth elements (REEs) in river and estuarine waters. By using natural waters as the reaction media (river water from the Connecticut, Hudson and Mississippi Rivers) geochemical reactions can be studied in isolation from the large temporal and spatial variability inherent in river and estuarine chemistry. Experiments, field studies and chemical models form a consistent picture whereby REE fractionation is controlled by surface/solution reactions. The concentration and fractionation of REEs dissolved in river waters are highly pH dependent. Higher pH results in lower concentrations and more fractionated composition relative to the crustal abundance. With increasing pH the order of REE adsorption onto river particle surfaces is LREEs > MREEs > HREEs. With decreasing pH, REEs are released from surfaces in the same order. Within the dissolved ( MREEs > LREEs, is most pronounced in the solution pool, defined here as MREEs > HREEs. While the large scale removal of dissolved river REEs in estuaries is well established, the release of dissolved REEs off river particles is a less studied process. Laboratory experiments show that there is both release and fractionation of REEs when river particles are leached with seawater. The order of sea water-induced release of dissolved REE(III) (LREEs > MREEs > HREEs) from Connecticut River particles is the same as that associated with lowering the pH and the same as that associated with colloidal particles. River waters, stripped of their colloidal particles by coagulation in estuaries, have highly evolved REE composition. That is, the solution pool of REEs in river waters are strongly HREE-enriched and are fractionated to the same extent as that of Atlantic surface seawater. This strengthens the conclusions of previous studies that the evolved REE composition of sea water is coupled to chemical weathering on the continents and reactions in estuaries. Moreover, the release of dissolved Nd from river particles to sea water may help to reconcile the incompatibility between the long oceanic residence times of Nd (7100 yr) and the inter-ocean variations of the Nd isotopic composition of sea water. Using new data on dissolved and particle phases of the Amazon and Mississippi Rivers, a comparison of field and laboratory experiments highlights key features of REE fractionation in major river systems. The dissolved pool of both rivers is highly fractionated (HREE enriched) with respect to the REE composition of their suspended particles. In addition, the dissolved pool of the Mississippi River has a large negative Ce-anomaly suggesting in-situ oxidation of Ce(III). One intriguing feature is the well developed maximum in the middle REE sector of the shale normalized patterns for the dissolved pool of Amazon River water. This feature might reflect competition between surface adsorption and solution complexation with carbonate and phosphate anions.

Late Neogene chronology: New perspectives in high-resolution stratigraphy

Abstract: We present an integrated geochronology for late Neogene time (Pliocene, Pleistocene, and Holocene Epochs) based on an analysis of data from stable isotopes, magnetostratigraphy, radiochronology, and calcareous plankton biostratigraphy. Discrepancies between recently formulated astronomical chronologies and magnetochronologies for the past 6 m.y. have been resolved on the basis of new, high-precision Ar/Ar ages in the younger part of this interval, the so-called Brunhes, Matuyama, and Gauss Epochs (5 Chrons C1n‐C2An; 0‐3.58 Ma), and revised analysis of sea floor anomalies in the Pacific Ocean in the older part, the so-called Gilbert Epoch (5 Chron C2Ar‐C3r; 3.58‐5.89 Ma). The magneto- and astrochronologies are now concordant back to the Chron C3r/C3An boundary at 5.89 Ma. TheNeogene(Miocene,Pliocene,Pleistocene, and Holocene) and Paleogene are treated here as period/system subdivisions oftheCenozoicEra/Erathem,replacements for the antiquated terms Tertiary and Quaternary.TheboundarybetweentheMiocene and Pliocene Series (Messinian/Zanclean Stages),whoseglobalstratotypesectionand point (GSSP) is currently proposed to be in Sicily,islocatedwithinthereversedinterval just below the Thvera (C3n.4n) Magnetic Polarity Subchronozone with an estimated age of 5.32 Ma. The Pliocene/Pleistocene boundary, whose GSSP is located at Vrica (Calabria,Italy),islocatednearthetopof the Olduvai (C2n) Magnetic Polarity Subchronozone with an estimated age of 1.81 Ma. The 13 calcareous nannoplankton and 48 planktonic foraminiferal datum events for the Pliocene, and 12 calcareous nannoplankton and 10 planktonic foraminiferal datum events for the Pleistocene, are calibrated to the newly revised late Neogeneastronomical/geomagneticpolarity time scale.

Climate-related variations in denitrification in the Arabian Sea from sediment 15N/14N ratios

Abstract: DENITRIFICATION—the process by which nitrate is reduced to gaseous nitrogen species (usually N2 or N2O)—is the dominant mechanism for removal of fixed nitrogen from the biosphere. In the oceans, denitrification is mediated by bacteria in suboxic environments and, by controlling the supply of fixed nitrogen, is an important limiting factor for marine productivity1–3. Denitrification produces substantial 15N enrichment in subsurface nitrate4–6, which is reflected in the isotopic composition of sinking particulate nitrogen7; sediment 15N/14N ratios in regions with suboxic water columns may therefore provide a record of past changes in denitrification intensity. Here we report nitrogen isotope data for sediment cores from three sites in the Arabian Sea. At all three sites we find large, near-synchronous downcore variations in 15N/14N, which are best explained by regional changes in the isotopic composition of subsurface nitrate, and hence denitrification. Moreover, these variations are synchronous with Milankovitch cycles, thereby establishing a link with climate. We argue that these large, climate-linked variations, in a region that contributes significantly to global marine denitrification, are likely to have perturbed marine biogeo-chemical cycles during the Late Quaternary period.

Finescale parameterizations of turbulent dissipation

Abstract: Fine- and microstructure data from a free fall profiler are analyzed to test models that relate the turbulent dissipation rate (e) to characteristics of the internal wave field. The data were obtained from several distinct been previously available. Observations from the ocean interior with negligible large-scale flow were examined to address the buoyancy scaling of e. These data exhibited a factor of 140 range in squared buoyancy frequency (N 2 ) with depth and uniform internal wave characteristics, consistent with the Garrett-Munk spectrum. The magnitude of e and its variation with N(∼N 2 ) was best described by the dynamical model of Henyey et al. A second dynamical model, by McComas and Muller, predicted an appropriate buoyancy scaling but overestimated the observed dissipation rates. Two kinematical dissipation parametrizations predicted buoyancy scalings of N 3/2 ; these are shown to be inconscient with the observations. Data from wave fields that depart from the canonical GM description are also examined an interpreted with reference to the dynamical models. The measurements came from a warm core ring dominated by strong near-inertial shears, a region of steep topography exhibiting high-frequency internal wave characteristics, and a midocean regime dominated at large wavelengths by an internal tide. Of the dissipation predictions examined, those of the Henyey et al. model in which eN − 2 scales as E 2 , where E is the nondimensional spectral shear level, were most consistent with observations. Nevertheless, the predictions for these cases exhibited departures from the observations by more than an order of magnitude. For the present data, these discrepancies appeared most sensitive to the distribution of internal wave frequency, inferred here from the ratio of shear spectral level to that for strain. Application of a frequency-based correction to the Henyey et al. model returned dissipation values consistent with observed estimates to within a factor of 2. These results indicate that the kinetic energy dissipation rate (and attendant turbulent mixing) is small for the background Garrett and Munk internal wave conditions (0.25eN −2 ∼ 0.7 × 10 − 5 m 2 s − 1). Dissipation and mixing become large when wave shear spectral levels are elevated, particularly by high-frequency waves. Thus, internal wave reflection/generation at steep topographic features appear promising candidates for achieving enhanced dissipation and strong diapycnal mixing in the deep ocean that appears required by box models and advection-diffusion balances

Growth of Prochlorococcus, a Photosynthetic Prokaryote, in the Equatorial Pacific Ocean

Abstract: The cell cycle of Prochlorococcus, a prokaryote that accounts for a sizable fraction of the photosynthetic biomass in the eastern equatorial Pacific, progressed in phase with the daily light cycle. DNA replication occurred in the afternoon and cell division occurred at night. Growth rates were maximal (about one doubling per day) at 30 meters and decreased toward the surface and the bottom of the ocean. Estimated Prochlorococcus production varied between 174 and 498 milligrams of carbon per square meter per day and accounted for 5 to 19 percent of total gross primary production at the equator. Because Prochlorococcus multiplies close to its maximum possible rate, it is probably not severely nutrient-limited in this region of the oceans.

Export production of particles to the interior of the equatorial Pacific Ocean during the 1992 EqPac experiment

Abstract: Twenty-four time-series, moored sediment traps were deployed between 2/2/92 and 1/27/93 along 140°W at 9°N, 5°N, 2°N, 0°, 2°S, 5°S and 12°S at water depths of approximately 1200 m and 2200 m, and 700 m above the bottom. The opening/closing of the traps was synchronized at 17-day periods, for 21 events, covering a total of 357 days. The average annual particle flux in the ocean's interior (2.2 to 4.4 km deep) from 5°N to 5°S was 28.5 g m−2 year−1, with 34.8 g−2 year−1 the maximum annual flux at the equator. Sixty-six per cent of settling particles were carbonate; 24% biogenic SiO2 and 5% organic carbon. The onset of tropical instability waves, marking the year's El Nino/post-El Nino boundary, was associated with a succession of intervals with greater organic carbon and opal at 5°N, 2°S and 5°S that occurred synchronously with a meridional oscillation of instability waves, while net carbon flux during El Nino and post-El Nino periods did not change. Although organic carbon flux increased at 5°N, 2°S and 5°S during the post-El Nino period, it was counterbalanced by decreases at the upwelling stations (2°N and the equator), resulting in no net carbon flux increase across the 5°N to 5°S region. In February/March 1992, only 0.34% of the organic carbon fixed by primary production over the 5°N to 5°S zone arrived in the ocean's interior. In August/September that year, zonal average of organic carbon flux increased slightly to 0.5% of primary production. Very little carbon reached the interior depths of the upwelling stations; however, the fraction of export was higher at the 5°N, 2°S and 5°S stations. The pattern of variability of particle flux at the shallow depths was observed also in deeper traps, without temporal offsets, suggesting a settling particle residence time shorter than the 17-day timeseries resolution during most of this experiment.

Hydrous, silica-rich melts in the sub-arc mantle and their relationship with erupted arc lavas

Abstract: Hydrous, silica-rich melts migrating through the mantle are preserved as glass inclusions in mantle minerals in xenoliths from Philippine arc lavas. These melts, with chemistries that indicate an origin by very low degrees of melting of the subducted ocean crust, have altered their host peridotites, yielding a metasomatized mantle. This 'fertilized' mantle is the source region of the arc magmas, which share continuous chemical trends with the melt inclusions, reflecting mixing and/or varying degrees of melting. These observations provide direct evidence for the importance of slab–mantle interactions in the genesis of island-arc magmas.

The internal structure of an active sea-floor massive sulphide deposit

Abstract: THE hydrothermal circulation of sea water through permeable ocean crust results in rock–water interactions that lead to the formation of massive sulphide deposits. These are the modern analogues of many ancient ophiolite-hosted deposits1–4, such as those exposed in Cyprus. Here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the Mid-Atlantic Ridge. A complex assemblage of sulphide–anhydrite–silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor. Indeed, the deposit grows largely as an in situ breccia pile, as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits. During inactive periods, the collapse of sulphide chimneys, dissolution of anhydrite, and disruption by faulting cause brecciation of the deposit. The abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures ( > 150 °C) currently maintained within the mound, and implies substantial entrainment of cold sea water into the interior of the deposit. These observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits, despite its absence in those preserved on land.

The contribution of microorganisms to particulate carbon and nitrogen in surface waters of the Sargasso Sea near Bermuda

Abstract: Seawater samples were collected from the euphotic zone of the Sargasso Sea near Bermuda in August of 1989 and March–April of 1990. Microbial population abundances, chlorophyll concentration, particulate carbon and particulate nitrogen were measured. Calculations were performed to establish the relative and absolute importance of the various microbial assemblages. The choice of conversion factors (g C and N cell −1 , or g C and N μm −3 ) for the microbial populations dramatically affected the estimation of “living” and “detrital” particulate material in the samples, and the relative importance of the various microbial groups. Averaged over all samples on either of the two cruises, microbial biomass constituted a greater proportion of the total particulate carbon and nitrogen during March–April (55% and 63%, respectively), than during August (≈24% and 30%, respectively) using “constrained” conversion factors that were derived. Accordingly, detrital material constituted the bulk of the particulate material during August, but was similar to the amount of microbial biomass during March–April. The bacterial assemblage constituted the largest single pool of microbial carbon (35%) and nitrogen (45%) in the water, and a significant fraction of the total particulate carbon (≈10–20%) and nitrogen (≈15–30%). Phototrophic nanoplankton (microalgae 2–20 μm in size) were second in overall biomass, and often dominated the microbial biomass in the deep chlorophyll maxima that were present during both cruises. The results temper recent assertions concerning the overwhelming importance of bacterial biomass in the oligotrophic Sargasso Sea but still support a major role for these microorganisms in the open ocean as repositories for carbon and nutrients.

The spray contribution to net evaporation from the sea: a review of recent progress

Abstract: The part that sea spray plays in the air-sea transfer of heat and moisture has been a controversial question for the last two decades. With general circulation models (GCMs) suggesting that perturbations in the Earth's surface heat budget of only a few W m−2 can initiate major climatic variations, it is crucial that we identify and quantify all the terms in that heat budget. Thus, here we review recent work on how sea spray contributes to the sea surface heat and moisture budgets. In the presence of spray, the near-surface atmosphere is characterized by a droplet evaporation layer (DEL) with a height that scales with the significant-wave amplitude. The majority of spray transfer processes occur within this layer. As a result, the DEL is cooler and more moist than the atmospheric surface layer would be under identical conditions but without the spray. Also, because the spray in the DEL provides elevated sources and sinks for heat and moisture, the vertical heat fluxes are no longer constant with height. We use Eulerian and Lagrangian models and a simple analytical model to study the processes important in spray droplet dispersion and evaporation within this DEL. These models all point to the conclusion that, in high winds (above about 15 m/s), sea spray begins to contribute significantly to the air-sea fluxes of heat and moisture. For example, we estimate that, in a 20-m/s wind, with an air temperature of 20°C, a sea surface temperature of 22°C, and a relative humidity of 80%, the latent and sensible heat fluxes resulting from the spray alone will have magnitudes of order 150 and 15 W/m2, respectively, in the DEL. Finally, we speculate on what fraction of these fluxes rise out of the DEL and, thus, become available to the entire marine boundary layer.

Land‐use change and the carbon cycle

Abstract: Changes in land use between 1850 and 1980 are estimated to have increased the global areas in croplands, pastures, and shifting cultivation by 891, 1308, and 30 × 106 ha, respectively, reducing the area of forests by about 600 × 106 ha, releasing about 100 PgC to the atmosphere, and transferring about 23 PgC from live vegetation to dead plant material and wood products. Another 1069 × 106 ha are estimated to have been logged during this period, and the net release of carbon from the combined processes of logging and regrowth contributed 23 PgC to the 100-PgC release. Annual rates of land-use change and associated emissions of carbon have decreased over the last several decades in temperate and boreal zones and have increased in the tropics. The average release of carbon from global changes in land use over the decade of the 1980s Is estimated to have been 1.6 ± 0.7 PgC y−1 almost entirely from the tropics. This estimate of carbon flux is higher than estimates reported in recent summaries because it is limited here to studies concerned only with changes in land use. Other recent analyses, based on data from forest inventories, have reported net accumulations of carbon as high as 1.1 PgC y−1 in temperate and boreal zones. Because the accumulation of carbon in forests may result from natural processes unrelated to land-use change, estimates based on these inventories should be distinguished from estimates based on changes in land use. Both approaches identify terrestrial sinks of carbon. The argument is made here, however, that differences between the two approaches may help identify the location and magnitude of heretofore ‘missing’ sinks. Before different estimates can be used in this way, analyses must consider similar geographical regions and dates, and they must account for the accumulation and loss of carbon in forest products in a consistent fashion.

Regional estimates of the export flux of particulate organic carbon derived from thorium-234 during the JGOFS EqPac program

Abstract: The upper ocean 234Th activity distribution at 77 stations was measured between 12°N and 10°S, and 95°W and 170°W in the spring and autumn of 1992. A regional scavenging model was used to estimate vertical export of particulate 234Th. Given the relatively high upwelling rates in this region, particularly at equatorial latitudes near 140°W, it was necessary to include upwelling of 234Th in our model in order to quantify particulate export. Using this export flux and the measured organic C or N to 234Th ratio on particles, one can empirically determine POC and PON fluxes for this region. The estimated particulate organic C flux varies spatially and temporally within this region, ranging from 1 to 7 mmol C m−2 day−1, with enhanced export occurring over the equator. Fluxes are also enhanced along 95°W coincident with a low temperature/high nutrient peak at 4°S. Along 140°W, particulate organic C export from the upper 100 m is on the order of 2 mmol C m−2 day−1 at latitudes beyond 4°N and 4°S, with an equatorial peak of 3–5 mmol C m−2 day−1 in both spring and fall. These results suggest that a relatively small per cent of the total production is exported locally on sinking particles (particle export/primary production C 234 Th ratios. Given the measured C N ratio, particulate N fluxes from the upper 100 m would be 6 times lower than for POC.

Long-term responses to factorial, NPK fertilizer treatment by Alaskan wet and moist tundra sedge species

Abstract: At thirteen sites in northern and central Alaska, full factorial and partial factorial NPK fertilizer experiments were completed in wet and moist tundras. The effects of the fertilizers on N and P concentrations in leaves, leaf mass per tiller, tillering, and flowering of the dominant sedge species (Eriophorum vaginatum, E. angustifolium, and Carex aquatilis) were documented for 3-10 yr at each site. Almost all sites showed at least some response to the fertilizer treatment, but the specific treatments and elements that caused the responses varied greatly among sites. There also was no consistent difference in responses between wet and moist sites. There was, however, a consistent temporal pattern to the responses observed, starting with increases in N and P concentration in leaves in the year that fertilizer was added, followed by growth and tillering responses in the second year, and increased flowering in the third year. The increases in N concentration generally only appeared in the first year, while increased P concentrations were sustained for 3-4 yr. Effects of fertilizer on flowering were still significant after 6 years in some cases. Results are discussed in terms of the role of "nutrient limitation" in ;:ucturing arctic plant communities and determining their productivity following disturbance or fertilization.

AinS and a new family of autoinducer synthesis proteins.

Abstract: In Vibrio fischeri, the autoinducer N-3-oxohexanoyl-L-homoserine lactone (AI-1) governs the cell density-dependent induction of the luminescence operon via the LuxR transcriptional activator. The synthesis of AI-1 from bacterial metabolic intermediates is dependent on luxI. Recently, we found a second V. fischeri autoinducer molecule, N-octanoyl-L-homoserine lactone (AI-2), that in E. coli also activates the luminescence operon via LuxR. A locus independent of luxI was identified as being required for AI-2 synthesis. This 2.7-kb ain (autoinducer) locus was characterized by transposon insertion mutagenesis, deletion and complementation analysis, and DNA sequencing. A single 1,185-bp gene, ainS, was found to be the sole exogenous gene necessary for the synthesis of AI-2 in Escherichia coli. In addition, a V. fischeri ainS mutant produced AI-1 but not AI-2, confirming that in its native species ainS is specific for the synthesis of AI-2. ainS is predicted to encode a 45,580-Da protein which exhibits no similarity to LuxI or to any of the LuxI homologs responsible for the synthesis of N-acyl-L-homoserine lactones in a variety of other bacteria. The existence of two different and unrelated autoinducer synthesis genes suggests the occurrence of convergent evolution in the synthesis of homoserine lactone signaling molecules. The C-terminal half of AinS shows homology to a putative protein in Vibrio harveyi, LuxM, which is required for the synthesis of a V. harveyi bioluminescence autoinducer. Together, AinS and LuxM define a new family of autoinducer synthesis proteins. Furthermore, the predicted product of another gene, ainR, encoded immediately downstream of ainS, shows homology to LuxN, which is similarly encoded downstream of luxM in V. harveyi and proposed to have sensor/regulator functions in the bioluminescence response to the V. harveyi auto inducer. This similarity presents the possibility that AI-2, besides interacting with LuxR, also interacts with AinR under presently unknown conditions.

Molecular evolution of the Alexandrium tamarense 'species complex' (Dinophyceae): Dispersal in the North American and West Pacific regions

Abstract: Hypotheses concerning the molecular evolution, population structure and dispersal of the toxic dinoflagellates Alexandrium tamarense (Lebour) Balech, A. catenella (Whedon et Kofoid) Balech and A. f...

Life in the fast lane: the life history of harbor porpoises from the gulf of maine

Abstract: We describe the life history of harbor porpoises in the Gulf of Maine by examining 239 animals killed in gill net fisheries and comparing these findings with the results of previous studies from the Bay of Fundy. Most female porpoises matured at age three and became pregnant each year thereafter. Reproduction was strictly seasonal, with ovulation, conception, and parturition occurring in the spring and early summer. The oldest specimen in the sample was 17 yr of age, but most individuals were younger than 12. The findings are similar to those of earlier studies from the Bay of Fundy and support the hypothesis that these animals form a single population. Harbor porpoises represent one end of a continuum of odontocete life histories that spans a wide diversity of strategies. In comparison with other, large odontocetes, harbor porpoises mature at an earlier age, reproduce more frequently, and live for shorter periods.