An official website of the United States government
Abstract Because of the pervasive role of water in the Earth system, the relative abundances of stable isotopologues of water are valuable for understanding atmospheric, oceanic, and biospheric processes, and for interpreting paleoclimate proxy reconstructions. Isotopologues are transported by both large‐scale and turbulent flows, and the ratio of heavy to light isotopologues changes due to fractionation that can accompany condensation and evaporation processes. Correctly predicting the isotopic distributions requires resolving the relationships between large‐scale ocean and atmospheric circulation and smaller‐scale hydrological processes, which can be accomplished within a coupled climate modeling framework. Here we present the water isotope‐enabled version of the Community Earth System Model version 1 (iCESM1), which simulates global variations in water isotopic ratios in the atmosphere, land, ocean, and sea ice. In a transient Last Millennium simulation covering the 850–2005 period, iCESM1 correctly captures the late‐twentieth‐century structure of δ18O and δD over the global oceans, with more limited accuracy over land. The relationship between salinity and seawater δ18O is also well represented over the observational period, including interbasin variations. We illustrate the utility of coupled, isotope‐enabled simulations using both Last Millennium simulations and freshwater hosing experiments with iCESM1. Closing the isotopic mass balance between all components of the coupled model provides new confidence in the underlying depiction of the water cycle in CESM, while also highlighting areas where the underlying hydrologic balance can be improved. The iCESM1 is poised to be a vital community resource for ongoing model development with both modern and paleoclimate applications.
more »
« less
On the Use of Dissolved Oxygen Isotopologues as Biogeochemical Tracers in the Northeast Pacific Ocean
Abstract The isotopic composition of dissolved oxygen offers a family of potentially unique tracers of respiration and transport in the subsurface ocean. Uncertainties in transport parameters and isotopic fractionation factors, however, have limited the strength of the constraints offered by18O/16O and17O/16O ratios in dissolved oxygen. To improve our understanding of oxygen cycling in the ocean's interior, we investigated the systematics of oxygen isotopologues in the subsurface Pacific using new data and a 2‐D isotopologue‐enabled isopycnal reaction‐transport model. We measured18O/16O and17O/16O ratios, as well as the “clumped”18O18O isotopologue in the northeast Pacific, and compared the results to previously published data. We find evidence that oxygen consumption in the northeast Pacific follows different mass‐dependent fractionation exponents from those typically used in oceanographic studies. These fractionation factors imply that an elevated proportion of17O compared to18O in dissolved oxygen—that is, its triple‐oxygen isotope composition—may not uniquely reflect only gross primary productivity and mixing. For all oxygen isotopologues, transport, respiration, and photosynthesis comprise important parts of their respective budgets. Mechanisms of oxygen removal in the subsurface ocean are discussed.
more »
« less
- Award ID(s):
- 1945316
- PAR ID:
- 10387923
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 127
- Issue:
- 12
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Stable oxygen isotopic ratios in corals (δ18Ocoral) are commonly utilized to reconstruct climate variability beyond the limit of instrumental observations. These measurements provide constraints on past seawater temperature, due to the thermodynamics of isotopic fractionation, but also past salinity, as both salinity and seawater δ18O (δ18Osw) are similarly affected by precipitation/evaporation, advection, and other processes. We use historical observations, isotope‐enabled model simulations, and the PAGES Iso2k database to assess the potential of δ18Ocoralto provide information on past salinity. Using ‘‘pseudocorals’’ to represent δ18Ocoralas a function of observed or simulated temperature and salinity/δ18Osw, we find that δ18Oswcontributes up to 89% of δ18Ocoralvariability in the Western Pacific Warm Pool. Although uncertainty in the δ18Osw‐salinity relationship influences the inferred salinity variability, corals from these sites could provide valuable δ18Oswreconstructions. Coordinated in situ monitoring of salinity and δ18Oswis vital for improving estimates of hydroclimatic change.more » « less
-
Abstract The isotopic composition of precipitation is used to trace water cycling and climate change, but interpretations of the environmental information recorded in central Andean precipitation isotope ratios are hindered by a lack of multi‐year records, poor spatial distribution of observations, and a predominant focus on Rayleigh distillation. To better understand isotopic variability in central Andean precipitation, we present a three‐year record of semimonthly δ18Opand δ2Hpvalues from 15 stations in southern Peru and triple oxygen isotope data, expressed as ∆′17Op, from 32 precipitation samples. Consistent with previous work, we find that elevation correlates negatively with δ18Opand that seasonal δ18Opvariations are related to upstream rainout and local convection. Spatial δ18Opvariations and atmospheric back trajectories show that both eastern‐ and western‐derived air masses bring precipitation to southern Peru. Seasonal d‐excesspcycles record moisture recycling and relative humidity at remote moisture sources, and both d‐excesspand ∆′17Opclearly differentiate evaporated and non‐evaporated samples. These results begin to establish the natural range of unevaporated ∆′17Opvalues in the central Andes and set the foundation for future paleoclimate and paleoaltimetry studies in the region. This study highlights the hydrologic understanding that comes from a combination of δ18Op, d‐excessp, and ∆′17Opdata and helps identify the evaporation, recycling, and rainout processes that drive water cycling in the central Andes.more » « less
-
The formation of the Isthmus of Panama closed the Central American Seaway, severing the only Late Cenozoic low‐latitude connection between the Pacific and Atlantic Oceans. Here we clarify the Early Pliocene (5.3–3.6 million years ago [Ma]) sequence of events associated with the shoaling of the Central American Seaway based on differences in upper ocean biogeochemical properties between the eastern tropical North Pacific (ETNP) and the Caribbean Sea. Foraminifera‐bound nitrogen isotopes (FB‐δ15N) are elevated in the ETNP relative to the Caribbean Sea throughout the Early Pliocene. Whereas ETNP FB‐δ15N shows no long‐term trend across the Early Pliocene, FB‐δ15N in the Caribbean Sea declines by ∼0.5‰ between 4.6 and 4.5 Ma, and by an additional ∼1‰ between 4.35 and 4.25 Ma. We interpret the divergence between ETNP and Caribbean Sea FB‐δ15N to indicate progressive isolation of their subsurface nutrient pools due to CAS shoaling. The oxygen isotopic composition of seawater (δ18Osw) derived from planktonic foraminiferδ18O and Mg/Ca shows a small but variable gradient between the ETNP and Caribbean Sea over the Early Pliocene, with a trend toward a largerδ18Oswgradient after 4.25 Ma. We suggest that the development of persistent chemical differences in both thermocline nutrients and surface waters between the ETNP and Caribbean Sea after 4.1 Ma reflects the cessation of basin‐scale oceanic exchanges across the Central American Seaway.more » « less
-
The sulfur chemistry of (162173) Ryugu particles can be a powerful tracer of molecular cloud chemistry and small body processes, but it has not been well explored. We report identification of organosulfurs and a sulfate grain in two Ryugu particles, A0070 and A0093. The sulfate grain shows oxygen isotope ratios (δ17O = −11.0 ± 4.3 per mil, δ18O = −7.8 ± 2.3 per mil) that are akin to silicates in Ryugu but exhibit mass-independent sulfur isotopic fractionation (Δ33S = +5 ± 2 per mil). A methionine-like coating on the sulfate grain is isotopically anomalous (δ15N = +62 ± 2 per mil). Both the sulfate and organosulfurs can simultaneously form and survive during aqueous alteration within Ryugu’s parent body, under reduced conditions, low temperature, and a pH >7 in the presence of N-rich organic molecules. This work extends the heliocentric zone where anomalous sulfur, formed by selective photodissociation of H2S gas in the molecular cloud, is found.more » « less
