Depletion Of Delta Research Articles

Hydrothermal Fluid Processes and Evolution of the Giant Serra Norte Jaspilite-Hosted Iron Ore Deposits, Carajas Mineral Province, Brazil

Hydrothermal Fluid Processes and Evolution of the Giant Serra Norte Jaspilite-Hosted Iron Ore Deposits, Carajas Mineral Province, Brazil

Resource switching in fish following a major food web disruption

Dreissenid mussels (Dreissena polymorpha and D. bugensis) have re-engineered Great Lakes ecosystems since their introduction in the late 1980s. Dreissenids can have major indirect impacts on profundal habitats by redirecting nutrients and energy away from pelagic production (which supplies profundal production) and depositing nutrients and energy in the nearshore zones that they occupy. However, strong empirical evidence for the effects of this redirection of resources on fish populations is currently lacking. Here, we report significant shifts in isotopic signatures, depth distribution and diets of a coldwater profundal fish population that are all consistent with a greater reliance on nearshore resources after the establishment of dreissenid mussels in South Bay, Lake Huron. Isotopic signatures of scales collected from 5-year-old lake whitefish (Coregonus clupeaformis) demonstrated remarkable stability over the 50-year period prior to the establishment of dreissenids (1947-1997) and a sudden and significant change in isotopic signatures (3 per thousand enrichment in delta13C and 1 per thousand depletion in delta(15)N) after their establishment (2001-2005). These dramatic shifts in isotopic signatures were accompanied by a coincident shift in the mean depth of capture of lake whitefish towards the nearshore. A comparison of previously unpublished pre-invasion diets of lake whitefish from South Bay with contemporary diets collected between 2002 and 2005 also indicate a greater reliance on nearshore prey after the invasion of dreissenid mussels. This study is the first to report changes in the carbon source available to lake whitefish associated with restructured benthic communities after the appearance of dreissenid mussels. Further, this study contributes to a growing body of work that demonstrates the ecological insights that can be gained through isotopic analysis of archived fish bony tissues in ecosystems that have experienced significant levels of disturbance.

Disentangling effects of growth and nutritional status on seabird stable isotope ratios

A growing number of studies suggest that an individual's physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather delta(15)N and delta(13)C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing delta(15)N and delta(13)C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in delta(15)N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC delta(15)N, with chicks exhibiting lower delta(15)N when they were growing the fastest. As growth slowed, delta(15)N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted delta(15)N in chick RBCs by 0.92 per thousand. We propose that increased nitrogen-use efficiency is responsible for (15)N depletion in both growing and food-restricted chicks. delta(15)N values in RBCs of free-ranging auklets fell within a range of only 1.03 per thousand, while feather delta(15)N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue.

Using δ15N and δ18O to evaluate the sources and pathways of NO in rainfall event discharge from drained agricultural grassland lysimeters at high temporal resolutions

The origin of NO(3) (-) yielded in drainage from agricultural grasslands is of environmental significance and has three potential sources; (i) soil organic mater (SOM), (ii) recent agricultural amendments, and (iii) atmospheric inputs. The variation in delta(15)N-NO(3) (-) and delta(18)O-NO(3) (-) was measured from the 'inter-flow' and 'drain-flow' of two 1 ha drained lysimeter plots, one of which had received an application of 21 m(3) of NH(4) (+)-N-rich agricultural slurry, during two rainfall events. Drainage started to occur 1 month after the application of slurry. The concentrations of NO(3) (-)-N from the two lysimeters were comparable; an initial flush of NO(3) (-)-N occurred at the onset of drainage from both lysimeters before levels quickly dropped to <1 mg NO(3) (-)-N L(-1). The isotopic signature of the delta(15)N-NO(3) (-) and delta(18)O-NO(3) (-) during the first two rainfall events showed a great deal of variation over short time-periods from both lysimeters. Isotopic variation of delta(15)N-NO(3) (-) during rainfall events ranged between -1.6 to +5.2 per thousand and +0.4 to +11.1 per thousand from the inter-flow and drain-flow, respectively. Variation in the delta(18)O-NO(3) (-) ranged from +2.0 to +7.8 per thousand and from +3.3 to +8.4 per thousand. No significant relationships between the delta(15)N-NO(3) (-) or delta(18)O-NO(3) (-) and flow rate were observed in most cases although delta(18)O-NO(3) (-) values indicated a positive relationship and delta(15)N-NO(3) (-) values a negative relationship with flow during event 2. Data from a bulked rainfall sample when compared with the theoretical delta(18)O-NO(3) (-) for soil microbial NO(3) (-) indicated that the contribution of rainfall NO(3) (-) accounted for 8% of the NO(3) (-) in the lysimeter drainage at most. The calculated contribution of rainfall NO(3) (-) was not enough to account for the depletion in delta(15)N-NO(3) (-) values observed during the duration of the rainfall event 2. The relationship between delta(15)N-NO(3) (-) and delta(18)O-NO(3) (-) from the drain-flow indicated that denitrification was causing enrichment in the isotopes from this pathway. The presence of slurry seemed to cause a relative depletion in delta(18)O-NO(3) (-) in the inter-flow and delta(15)N-NO(3) (-) in the drain-flow compared with the zero-slurry lysimeter. This may have been caused by increased microbial nitrification stimulated by the presence of increased NH(4) (+)-N.

Palaeovolcanic forcing of short-term dendroisotopic depletion: The effect of decreased solar intensity on Irish oak

[1] The climatic effects of historical volcanic eruptions are well documented in the literature. What are less certain however, are the effects of eruptions on more distant environments, particularly vegetation. Here we present subannual delta(13)C records from two high-resolution Irish oak ( Quercus spp.) chronologies that span the Laki (Grimsvotn) 1783-84 and Tambora 1815 eruptions. In both instances, a significant depletion in delta(13)C is recorded within the trees following the eruption (similar to 1.8%o). Historical meteorological datasets from observatories near to the trees sampled demonstrate that the shifts in carbon isotopic content cannot be accounted for by changes in local climate. We postulate atmospheric loading of ejecta from the eruptions resulted in significantly reduced irradiance, increasing discrimination within the trees.

The Formation of Septarian Concretions in Queen Charlotte Islands, B.C.: Evidence for Microbially and Hydrothermally Mediated Reactions at Shallow Burial Depth

Petrographic, chemical and isotopic studies of marine sediment-hosted septarian concretions from Lower Jurassic Whiteaves Formation in the Queen Charlotte Islands, B.C., Canada, reveal a complex diagenetic history that has resulted from bacterially mediated reactions at shallow burial depth as well as hydrothermally modified meteoric waters. The general diagenetic sequence in cement-filled septaria cracks includes: 1) fibrous calcite, 2a) bladed calcite or 2b) ferroan saddle-like calcite, 3) blocky calcite with early ferroan and late non-ferroan stages, and 4) barite. Each cement generation has a characteristic chemical and isotopic signature. Oxidation of upward-diffused methane contributed to an extremely negative value ofdelta C (ca. -35 per thousand ) in the early generation of fibrous calcite. The delta O (ca. -3.0 per thousand ) and 87 Sr/ 86 Sr (0.70683) values of these calcites, however, reflect Jurassic seawater composition. Plutonism during Late Jurassic to Early Cretaceous time provided hydrothermal discharge that altered meteoric waters. This process became the main factor for the precipitation of saddle-like and bladed calcites. These two generations of carbonate cement are characterized by relative depletion in delta 18 O (-11.5 to -17.4 per thousand ) and less radiogenic 87 Sr/ 86 Sr (0.70532 to 0.70575) signatures. Progressive modification in pore water chemistry and increasing depth of burial occurred during the formation of late ferroan blocky calcite.

Structural setting and fluid characteristics of the Proterozoic Tartan Lake gold deposit, Trans-Hudson Orogen, northern Manitoba

The late-kinematic structural architecture of the Flin Flon domain is dominated by a network of anastomosing shear zones formed by compressional deformation during the Proterozoic Trans-Hudson orogeny (ca. 1900-1800 Ma). A number of structurally controlled mesothermal gold deposits occur throughout the region, associated with this shear zone network. The Tartan Lake gold deposit occurs in the Tartan Lake shear zone, at the contact between a layered gabbroic intrusive complex and metavolcanic rocks of the Amisk group (ca. 1875 Ma).Five phases of deformation have been recognized in the Flin Flon region (P1-P5). Midgreenschist facies peak metamorphic conditions (phase 3) at Tartan Lake are recorded by a mineral assemblage of biotite-actinolite-albite-muscovite-epidote and carbonate in volcani-clastic rocks, along with a well-developed phase 3 schistosity. Early movement of the Tartan Lake shear zone was initiated with phase 3 deformation, during which oblique slip occurred. During phase 4, this shear zone was overprinted by a major regional fold and the shear zone was reactivated by strike-slip movement. Regional phase 3 schistosity is refolded in a series of steeply plunging mesoscopic phase 4 fold closures that were synchronous with the shear zones.A network of conjugate strike-slip shear zones that vary in width from 5 to 35 m comprise the 0.3-km-wide structure at Tartan Lake. Deformation within the shear zones is marked by (1) development of S and C schistosities in which C is dominant, (2) weakly developed sub-horizontal mineral lineations, and (3) folding and kink banding of these schistosities. Within shear zones, sericite, chlorite, quartz, carbonate, albite, tourmaline, and pyrite are the dominant minerals and biotite and actinolite are retrograded to chlorite, such that this deformation and Au mineralization are postpeak metamorphism. Five stages of veining occurred within the shear zones, and these are characterized by distinctive orientations and mineral parageneses. Gold mineralization occurred with two of these stages of veining, along with pyrite, chalcopyrite, tellurides, monazite, scheelite, and rutfie. The timing of this mineralizing event has been constrained by the 40 Ar/ 39 Ar method at 1791 + or - 4 Ma; this is 20 to 40 m.y. postpeak metamorphism.Fluids were of H 2 O-CO 2 -NaCl composition throughout the ore-forming vein events, with modal salinity = 6.9 wt percent equiv, CO 2 density = 0.64 g/cm 3 , and homogenization temperatures ranging from 250 degrees to 390 degrees C (with a median of 295 degrees C). Stable isotope compositions of quartz (delta 18 O = 10.8-13.8ppm), chlorite (delta 18 O = 3.0-4.8ppm), muscovite (delta 18 O = 7.5-9.0ppm), scheelite (delta 18 O = 4.0-5.0ppm), albite (delta 18 O = 9.0-9.6ppm), tourmaline (delta 18 O = 7.9-8.8ppm), pyrite (delta 34 S = 1.7-3.1ppm), and chalcopyrite (delta 34 S = 1.4-1.7ppm) establish the temperature of gold mineralization between 315 degrees and 472 degrees C, with an average at 372 degrees + or - 41 degrees C (1Sigma ). Ore-forming fluids had delta 18 O = 5.2 to 6.5 per mil and delta D = -50 to -86 per mil, and Fe dolomites from mineralized veins exhibit restricted ranges of delta 13 C (-7.0 to -5.2ppm and delta 18 O (9.3 to 10.9ppm),suggesting a uniform fluid composition. These veins formed at a pressure of 1.2 to 2.4 kbars, corresponding to 4.3 to 8.6 km, if lithostatic fluid pressure is assumed.Constraints on the depth at which these veins precipitated and the character of the fluids suggest that this gold deposit formed from advecting metamorphic fluids. A postmineralization stage of brittle fracturing is represented by barren veins that exhibit significant depletion in delta 34 S (-29 to -30ppm). This may be the result of an increase in fluid f (sub O 2 ) in the final stages of crustal deformation during the Trans-Hudson orogeny.