Climate regime shifts force fish communities through rapid transitions between alternate species assemblages, but little is known about the role that biochemical ecology plays in these transitions. ...We document a biochemical effect of climate-induced community transitions in boreal oceans: opposite population trajectories of lipid-rich and lipid-poor fish species. We compared published estimates of fish lipid content and population trajectories following climate shifts in 4 areas (Bering Sea, Gulf of Alaska, Scotian Shelf and North Sea). In all cases, total lipid content differed between species that increased and decreased in abundance, and the resulting relatively lipid-rich or lipid-poor communities persisted for decades. We hypothesize that these changes in fish community lipid content are the result of climate-mediated changes in the availability of essential fatty acids (EFAs), which are required by fish as components of hormones and cell membranes. EFAs are produced only by plants and must be obtained by fish through their diet, and ecosystem EFA availability is sensitive to physical forcing mechanisms. Using original data from 5 species of northeast Pacific fish (total lipid 1.0 to 28.9% wet mass) and published data for 29 species of myctophids (total lipid 0.5 to 46.3% wet mass), we found that the content of 2 important EFAs was positively correlated with total lipid content. This result suggests the possibility of species differences in EFA requirements that are related to total lipid content, and possible differences in susceptibility to changing EFA availability in lipid-rich and lipid-poor fish species.
The Formula: see text index is widely used to infer paleo-sea surface temperatures from the relative abundances of sedimentary 37:3 and 37:2 methyl alkenones. However, the measurements can be ...difficult and error prone when the alkenones are present in only trace amount, when one is much more abundant than the other, or when co-eluting compounds are present. Silylated alkenols can be analyzed by way of gas chromatography–electron ionization mass spectrometry (GC–EIMS) with much greater sensitivity and specificity than the parent alkenones and near-baseline resolution can be obtained without the use of very long chromatographic columns and/or slow temperature programs. We show, using particulate matter from the Black Sea and the DYFAMED site in the Ligurian Sea, and surface sediments from the Black Sea and SE Alaska, that conversion of C₃₇ alkenones to alkenols using NaBH₄ reduction and subsequent derivatization to TMSi ethers allows Formula: see text values to be reliably calculated without time consuming purification steps, using the relative abundances of the diagnostic m/z 117 ion. The response factor for m/z 117 varies for 37:3 and 37:2 alkenols, so a specific correction is required. The reduction method is easy to use, highly sensitive and widely applicable. Ethyl alkenols give a characteristic ion at m/z 131 and, if NaBD₄ is used, the ions at m/z 117 and 131 shift to m/z 118 and 132, providing further confirmation of the structures.
In our study of Station ALOHA, a site representative of the oligotrophic North Pacific subtropical gyre (NPSG), alkenone content and composition were examined in (1) sinking particulate materials ...collected in sediment traps moored at 2800
m during 2 year-long deployments (1992–1993 and 2000–2001) and (2) suspended particulate materials collected throughout the euphotic zone in two contrasting seasons (winter and summer). Each year, sediment trap records documented pronounced alkenone export events in both seasons. The winter event appears triggered by eddy diffusive mixing of nutrients into the upper water column and the release of light limitation on alkenone-producing photoautotrophs growing in the deep chlorophyll maximum layer (DCML). The summer event originates apparently from a stratified euphotic depth well above the DCML where others have now documented the occurrence of N
2 fixation-based ‘new production’. Although our time series record is yet limited, it is likely that the absolute magnitude of alkenone export and its quantitative importance in winter relative to summer is an ecological feature of the NPSG which can oscillate significantly on decadal time scales in response to climatic forcing. Despite the significant seasonal and interannual differences in alkenone export noted in our study, findings suggest that paleotemperature assessments based on analysis of the alkenone unsaturation index
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measured in underlying sediments would likely be unimpaired by the higher frequency temporal variability in the surface water ecology of alkenone-producers. When translated using a widely accepted calibration equation (
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=0.034
T+0.039),
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values in average sediment trap particles are consistent with the mean annual sea-surface temperature at Station ALOHA.
C
37–39 alkenones and C
36 alkenoates, biomarkers of haptophyte origin, were measured in a 10-month sediment trap times series from the Wilkinson Basin in the Gulf of Maine (GOM). Highest biomarker ...flux to the seabed was observed in summertime, the period when surface waters are stratified and a persistent, subsurface chlorophyll maximum (SCM) exists within the upper thermocline and at the base of the euphotic zone throughout the GOM. Comparison of biomarker content and composition of sediment trap particles and underlying surface sediments indicates significant loss (>50%) of signal due to the impact of early diagenesis. Despite such loss, however, C
37 alkenone unsaturation patterns (
U
37
K′) are not altered. Estimates of algal growth temperature made from analysis of
U
37
K′ in these sedimentary materials correspond with water temperature measured at the SCM, identifying this biological oceanographic feature as a key site of alkenone export production to the GOM sediment record. Given the common occurrence of SCM in surface waters of the world ocean, particularly the expansive oligotrophic regions of the subtropical to temperate ocean, export of alkenones produced within such features is a potentially widespread biological oceanographic phenomenon which shapes the sediment record for these biomarkers.
The record for plankton biomarkers in sediment trap samples from a one-year experiment in the central Arabian Sea (AS4: 15°59′N 61°30′E) shows variations that reflect changing biological conditions ...in surface waters. Particulate fluxes of C
37–39 alkenones, highly branched C
25 isoprenoids (HBI), dinosterol,
nC
28 12-hydroxy fatty acid, 24-ethylcholesterol, and a C
30–34 series of pentacyclic triterpanols all displayed distinct maxima at the start and stop of the Northeast (NE) and Southwest (SW) Monsoons. Surface mixing conditions changed rapidly at these times, altering light and nutrient availability, thereby triggering these biomarker signals of export production. Temporal offsets noted in individual biomarker concentrations (per g total organic carbon) at the start of the SW Monsoon suggest succession occurs in the phytoplankton community contributing to organic matter export. Comparable offsets were neither apparent at the start of the less dynamic NE Monsoon nor at the end of the NE or SW Monsoons. Broad concentration maxima for HBI also were observed at the beginning and end of the time-series during the relatively quiescent Fall Intermonsoon period when such features were conspicuously absent for other biomarkers. HBI are reputed biomarkers of
Rhizoselenia and
Haslea spp., two recognized dominants of diatom biomass in the Arabian Sea. These peaks in biomarker concentration could reflect either changes in the relative proportion of specific organisms that contribute to the upper ocean productivity or enhanced preservation of the biomarkers during times of high export production. In either case, the biomarker record in sediment traps reflects important changes in the biological condition of the upper ocean.
All biomarkers except HBI were measurable in surface sediments deposited beneath the trap site. Comparison with concentrations in average sediment trap particles showed each was sensitive to significant (∼99%) degradation, displaying depletion factors relative to TOC of ⩾4. Clearly, consequences of such high levels of early diagenetic recycling must be considered carefully when conclusions about changes in export production from surface waters in past oceans are drawn from stratigraphic analysis of biomarkers in marine sediments.
The elemental and major biochemical compositions of the relict f-turbidite sampled in two cores from the Madeira Abyssal Plain were determined. This fine-grained, distal sequence occurs at ca. 9 m ...core depth and includes a surficial oxidized horizon defined by a distinct color change. Oxygen diffused downward through sediments above this interface and in ca. 10 kyr destroyed 80% of the organic substances that below the front had survived degradation in the presence of porewater sulfate for ca. 140 kyr. These deposits provide an opportunity to establish the extent and selectivity of oxic sedimentary degradation under natural conditions without the usual complications of bioturbation and varying sources or sedimentation rates.
In both cores, a sample from the upper oxidized layer was compared to two samples from the underlying unoxidized layers. The unoxidized sequences of both turbidities contained 0.93–1.02 wt% organic carbon (OC) and 0.10–0.11 wt% total nitrogen (TN). Approximately 20% of the initial OC and 40% of the initial TN remained in the oxidized horizons, with a consequent decrease in atomic C/N ratio from ca. 11 to ca. 5. All samples gave very low yields of lignin phenols and comparable OC-normalized yields of total aldoses and amino acids, and indicated predominantly marine organic matter (OM) and nonselective oxic degradation of these biochemical classes. Compositions of individual aldoses and amino acids generally were also similar in surface and deep sediments, except that the oxidized horizons yielded markedly elevated (3–5X) percentages of nonprotein amino acids. This study clearly demonstrates that prolonged exposure to OZ can lead to organic matter alteration which is far more extensive than that obtained with sulfate alone. In comparison to early diagenesis, however, alteration of the measured biochemicals was largely nonselective. Such oxidation reactions could control the distribution and composition of organic matter in slowly accumulating continental rise and deep-ocean environments.
A set of oxidized and unoxidized sediment intervals from the f-turbidite identified in two piston cores from the Madeira Abyssal Plain (MAP) was analyzed for calcium carbonate, total organic carbon ...(TOC), total nitrogen (TN), stable carbon composition of TOC (
δ
13C
toc
), total hydrolyzable amino acids (THAA), total neutral sugars (TSUG), lignin phenols (LIG), two different lipid biomarkers of marine phytoplankton origin and vascular plantwax
n-alkanes and
n-acids. Comparison shows changes for all properties depicting the effect of post-depositional, aerobic oxidation. The oxidation process re-mineralized approximately 80% of the TOC and approximately 60% of the TN in the original deposit and left the residual organic matter depleted in
13C by 1.7–2.9‰ THAA and TSUG account for 10% or less of the TOC in all samples leaving approximately 90% of the TOC chemically unidentified. THAA, TSUG, LIG, marine phytoplankton biomarkers and plantwax
n-acids were lost from the oxidized deposit to an extent as great as that for TOC. Two non-protein amino acids (β-alanine and γ-aminobutyric acid) and plant wax
n-alkanes displayed much less degradation (9–37%) and concentrated 3.3–4.8 times relative to TOC by the oxidation process. These observations show that both marine and terrestrial components contribute to the re-mineralized TOC fraction. A binary mixing approach was used to model quantitatively the change in
δ
13C
toc
and plantwax
n-alkane concentration. Results suggest that terrestrial organic carbon contributes approximately 15% to the TOC content of the original turbidite, its abundance increases approximately 2–4 times as a consequence of the oxidation process and approximately 40 and 90% of the terrestrial and marine component of TOC in the original turbidite, respectively, was destroyed by the oxidation process. Although selective preservation of terrestrial relative to marine organic carbon is a well-documented phenomenon in sedimentary processes, this study represents the first attempt to assess the sensitivity of terrestrial organic matter to oxidative degradation in a sedimentary environment.
An empirical global core-top calibration that relates the alkenone unsaturation index
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to mean annual SST (maSST) is statistically the same as that defined for a subarctic Pacific strain of
...Emiliania huxleyi (CCMP1742) grown exponentially in batch culture under isothermal conditions. Although both equations have been applied widely for paleoSST reconstruction, uncertainty still stems from two key ecological factors: variability in the details of biosynthesis among genetically distinct alkenone-producing strains, and impacts of non-thermal physiological growth factors on
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. New batch culture experiments with CCMP1742 here reveal that
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diverge systematically from the core-top calibration in response to nutrient depletion and light deprivation, two physiological stresses experienced by phytoplankton populations in the real ocean. Other aspects of alkenone/alkenoate composition also respond to these stresses and may serve as signatures of such effects, providing an opportunity to detect, understand, and potentially correct for such impacts on the geologic record. A test case documents that sediments from the Southeast Pacific display the alkenone/alkenoate compositional signature characteristic of cells physiologically stressed by light deprivation. Such an observation could be explained if marine snow provided a major vector of sedimentation for these biomarkers. Late Pleistocene
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records in the Southeast Pacific yield plausible paleotemperature histories of ice-age cooling, but ice-age alkenone/alkenoate signatures fall outside the range of modern calibration samples of similar
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. They better match core-top samples deposited beneath waters characterized by much cooler maSST, suggesting key features of ice-age ecology for alkenone-producing haptophytes were different from today, and that the
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index taken alone may misgauge the total range of ice-age cooling at these locations. Analysis of the full spectrum of alkenone/alkenoate compositions preserved in sediments opens up a new opportunity that may improve the accuracy of paleotemperature estimates based on simple
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analysis and help resolve longstanding disagreements between various paleotemperature reconstruction methods.
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