Wilbert Weijer

Los Alamos National Laboratory | LANL · Computer, Computational, and Statistical Sciences Division

Plain Language Summary The Beaufort Gyre (BG) has increased its liquid freshwater content (FWC) by 40% in the past two decades. If released and transported downstream to the subpolar North Atlantic Ocean, the excess water might affect the ocean circulation via suppression of deep‐water formation. However, which layer is responsible for BG freshwate...

In this paper we introduce a new software framework for the offline calculation of tracer transport in the ocean. The Fast Equilibration of Ocean Tracers Software (FEOTS) is an end-to-end set of tools to efficiently calculate tracer distributions on a global or regional sub-domain using transport operators diagnosed from a comprehensive ocean model...

The Energy Exascale Earth System Model (E3SM) is a state-of-the-science Earth system model (ESM) with the ability to focus horizontal resolution of its multiple components in specific areas. Regionally refined global ESMs are motivated by the need to explicitly resolve, rather than parameterize, relevant physics within the regions of refined resolu...

The Atlantic Meridional Overturning Circulation (AMOC) plays a significant role in the global climate system, and its behavior in a warming climate is a matter of significant concern. The AMOC is thought to be driven largely by ocean heat loss in the subpolar North Atlantic Ocean, but recent research increasingly emphasizes the importance of the Ar...

The Energy Exascale Earth System Model (E3SM) is a state-of-the-science Earth system model (ESM) with the ability to focus horizontal resolution of its multiple components in specific areas. Regionally refined global ESMs are motivated by the need to explicitly resolve, rather than parameterize, relevant physics within the regions of refined resolu...

The Beaufort Gyre (BG), the largest Arctic Ocean freshwater reservoir, has drastically increased its liquid freshwater content by 40% in the past two decades. If released within a short period, the excess freshwater could potentially impact the large-scale ocean circulation by freshening the upper subpolar North Atlantic. Here, we track BG-sourced...

Larger Weddell Sea polynyas (WSPs), differentiated in this study from the smaller Maud Rise Polynyas (MRPs), forming to the east of the prime meridian in the proximity of the Maud Rise seamount, have last been observed in the 1970s. We investigate WSPs that grow realistically out of MRPs in a high-resolution (HR) preindustrial simulation with the E...

We use a modern Earth system model to approximate the relative importance of ice versus temperature on Arctic marine ecosystem dynamics. We show that while the model adequately simulates ice volume, water temperature, air‐sea CO2 flux, and annual primary production in the Arctic, itunderestimates upper water column nitrate across the region. This n...

The Zapiola Anticyclone (ZA) is a strong, O(100 Sv), barotropic vortex in the center of the Argentine Basin that is tied to a bathymetric feature called the Zapiola Rise. It is regionally significant for two reasons: first, the strong vortex is a dynamical barrier that inhibits the lateral exchange of water, and hence has the ability to trap water...

Plain Language Summary The Atlantic Meridional Overturning Circulation (AMOC) is a circulation pattern in the Atlantic Ocean that is an important component of the climate system, due to its ability to redistribute and sequester heat and carbon. An accurate representation of the AMOC is a critical test for climate models and essential for building c...

The Atlantic meridional overturning circulation (AMOC) represents the zonally integrated stream function of meridional volume transport in the Atlantic Basin. The AMOC plays an important role in transporting heat meridionally in the climate system. Observations suggest a heat transport by the AMOC of 1.3 PW at 26°N ‐ a latitude which is close to wh...

As the greenhouse gas concentrations increase, a warmer climate is expected. However, numerous internal climate processes can modulate the primary radiative warming response of the climate system to rising greenhouse gas forcing. Here the particular internal climate process that we focus on is the Atlantic Meridional Overturning Circulation (AMOC)...

Weddell Sea open-ocean polynyas have been observed to occasionally release heat from the deep ocean to the atmosphere, indicating that their sporadic appearances may be an important feature of high-latitude atmosphere-ocean variability. Yet, observations of the phenomenon are sparse and many standard resolution models represent these features poorl...

Climate scientists collaborated in a nationwide event to analyze and compare archived Earth system model simulations and to generate input for the IPCC's upcoming climate change report.

Since near‐term predictions of present‐day climate are controlled by both initial condition predictability and boundary condition predictability, initialized prediction experiments aim to augment the external‐forcing‐related predictability realized in uninitialized projections with initial‐condition‐related predictability by appropriate observation...

Abstract We document the configuration, tuning, and evaluation of a modified version of the Community Earth System Model version 1 (Hurrell et al., 2013, https://doi.org/10.1175/BAMS-D-12), introduced here as E3SMv0‐HiLAT, intended for study of high‐latitude processes. E3SMv0‐HiLAT incorporates changes to the atmospheric model affecting aerosol tra...

The notion that the Atlantic Meridional Overturning Circulation (AMOC) can have more than one stable equilibrium emerged in the 1980s as a powerful hypothesis to explain rapid climate variability during the Pleistocene. Ever since, the idea that a temporary perturbation of the AMOC—or a permanent change in its forcing—could trigger an irreversible...

Open ocean polynyas (OOPs) in the Southern Ocean are ice-free areas within the winter ice pack that are associated with deep convection, potentially contributing to the formation of Antarctic Bottom Water. To enhance the credibility of Earth System Models (ESMs), their ability to simulate OOPs realistically is thus crucial. Here we investigate OOPs...

Evidence for the assumptions of the salt-advection feedback in box models is sought by studying the At- lantic meridional overturning circulation (AMOC) internal variability in the long preindustrial control runs of two Earth system models. The first assumption is that AMOC strength is proportional to the meridional density difference between the N...

In this paper we study upwelling pathways and timescales of Circumpolar Deep Water (CDW) in a hierarchy of models using a Lagrangian particle tracking method. Lagrangian timescales of CDW upwelling decrease from 87 years to 31 years to 17 years as the ocean resolution is refined from 1° to 0.25° to 0.1°. We attribute some of the differences in time...

The original version of this Article contained errors in Fig. 6. In panel a, the grey highlights obscured the curves for CESM, CM2.6 and SOSE, and the labels indicating SWIR, KP, MR, PAR, and DP were inadvertently omitted. These have now been corrected in both the PDF and HTML versions of the Article.

Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocea...

In this paper the atmospheric response to an open-ocean polynya in the Southern Ocean is studied by analyzing the results from an atmospheric and oceanic synoptic-scale resolving Community Earth System Model (CESM) simulation.While coarser-resolution versions of CESMgenerally do not produce open-ocean polynyas in the SouthernOcean, they do emerge a...

The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, 'Agulhas leakage', forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for th...

Supplementary Figures 1-6

Fossils of marine microorganisms such as planktic foraminifera are among the cornerstones of palaeoclimatological studies. It is often assumed that the proxies derived from their shells represent ocean conditions above the location where they were deposited. Planktic foraminifera, however, are carried by ocean currents and, depending on the life tr...

In this study we address the question whether eddy-driven transports in the Argentine Basin can be held responsible for enhanced sediment accumulation over the Zapiola Rise, hence accounting for the existence and growth of this sediment drift. To address this question, we perform a 6-year simulation with a strongly eddying ocean model. We release t...

The strongly eddying version of the Parallel Ocean Program (POP) is used in two 45-yr simulations to investigate the response of the Atlantic meridional overturning circulation (AMOC) to strongly enhanced freshwater input due to Greenland melting, with an integrated flux of 0.5 Sverdrups (Sv; 1 Sv equivalent to 10(6) m(3) s(-1)). For comparison, a...

The impact of Agulhas leakage variability on the strength of the Atlantic meridional overturning circulation (AMOC) in the Community Climate System Model, version 4 (CCSM4) is investigated. In this model an advective connection exists that transports salinity anomalies from the Agulhas region into the North Atlantic on decadal (30-40 yr) time scale...

Agulhas Leakage is an important link in the global ocean circulation, as it transfers a significant volume of relatively warm and salty water from the Indian Ocean to theAtlantic Ocean. The main route of this transfer is through the shedding of large Agulhas rings from the Agulhas retroflection. In this paper we study the dynamics of the ring forma...

A systematic study is presented of decadal climate variability in the North Pacific. In particular, the hypothesis is addressed that oceanic Rossby basin modes are responsible for enhanced energy at decadal and bidecadal time scales. To this end, a series of statistical analyses are performed on a 500-yr control integration of the Community Climate...

This study analyzes important aspects of the tropical Atlantic Ocean from simulations of the fourth version of the Community Climate System Model (CCSM4): the mean sea surface temperature (SST) and wind stress, the Atlantic warm pools, the principal modes of SST variability, and the heat budget in the Benguela region. Themain goal was to assess the...

The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to high-latitude freshwater input is one of the key uncertainties in the climate system. Considering the importance of the AMOC for global heat transports, and the vulnerability of the Greenland Ice Sheet (GrIS) to global warming, assessing this sensitivity is critical for cl...

The new Community Climate System Model, version 4 (CCSM4), provides a powerful tool to understand and predict the earth's climate system. Several aspects of the Southern Ocean in the CCSM4 are explored, including the surface climatology and interannual variability, simulation of key climate water masses (Antarctic Bottom Water, Subantarctic Mode Wa...

The Atlantic Meridional Overturning Circulation (AMOC) is an integral part of the circulation in the Atlantic Ocean. The AMOC is typically characterized by the meridional streamfunction, which is also an indicator of the thermohaline circulation. This paper explores the mean state and long-term variability of the Atlantic meridional streamfunction...

The Agulhas leakage to the South Atlantic exhibits a strong anti-correlation with the mass flux of the Agulhas Current. When the Agulhas retroflection is in its normal position near Cape Agulhas, leakage is relatively high and the nearby South African coastal slant (angle of derivation from zonal) is very small and relatively invariant alongshore....

The sensitivity of the Meridional Overturning Circulation (MOC) to a freshwater discharge in the northern North Atlantic is a matter of concern, considering the threat that global warming poses to the stability of the Greenland ice sheet. Understanding the processes through which an enhanced freshwater discharge affects the MOC is therefore importa...

Agulhas leakage, the transport of Agulhas Current water from the Indian Ocean to the Atlantic Ocean, has been shut off during past glacial periods, a phenomenon tentatively ascribed to northward migration of westerly wind bands. At present, the leakage is significant and its magnitude exhibits an anti-correlation with the current's incoming mass fl...

The Agulhas leakage to the South Atlantic exhibits a strong anti-correlation with the mass flux of the Agulhas Current. When the Agulhas retroflection is in its normal position near Cape Agulhas, leakage is relatively high and the nearby South African coastal slant (angle of derivation from zonal) is very small and relatively invariant alongshore....

1] The Australian‐Antarctic Basin (AAB) is known for its high levels of intraseasonal variability; sea‐surface height variability exceeds background values by factors of 2 over thousands of kilometers. This paper addresses the hypothesis that this variability is caused by trapping of barotropic energy by the basin geometry. Analysis of a multi‐year...

The barotropic intraseasonal variability in the Australia–Antarctic Basin (AAB) is studied in terms of the excitation and decay of topographically trapped barotropic modes. The main objective is to reconcile two widely differing estimates of the decay rate of sea surface height (SSH) anomalies in the AAB that are assumed to be related to barotropic...

A framework for a fully implicit solution method is imple- mented into (1) the High Order Methods Modeling Environment (HOMME), which is a spectral element dynamical core option in the Community Atmosphere Model (CAM), and (2) the Parallel Ocean Pro- gram (POP) model of the global ocean. Both of these models are com- ponents of the Community Climat...

We employ a suite of methods to study the excitation and decay of topographically-trapped Rossby modes in the Australia-Antarctic Basin (AAB). These modes provide an efficient way to funnel wind energy to the abyss due to their barotropic nature. A normal mode analysis in a shallow-water model identifies two modes that are responsible for most of t...

In this paper the origin of the bi-monthly variability in the Mascarene Basin is reconsidered. Free oscillatory modes of the Mascarene Basin are determined by performing normal mode analysis on the motionless solution in a barotropic shallow-water model with realistic bathymetry. Several modes are identified with monthly to bi-monthly time scales....

Observations of the sea surface height in the Argentine Basin indicate that strong variability occurs on a time scale of 20−30 days. The aim of this study is to determine the physical processes responsible for this variability. First, results are presented from two statistical techniques applied to a decade of altimetric data. A complex empirical o...

In this paper the spectrum of barotropic basin modes of the Argentine Basin is shown to be connected to the classical Rossby basin modes of a flat-bottom (constant depth), rectangular basin. First, the spectrum of basin modes is calculated for the Argentine Basin, by performing a normal-mode analysis of the barotropic shallow-water equations. Then...

Recent observations in the Argentine Basin indicate that strong oscillations occur on a time scale of 20-30 days. Here we show that multiple oscillatory modes may be present in the Argentine Basin, reconciling several apparently conflicting estimates of the dominant time scale. First, results are presented from two statistical techniques applied to...

The response of the Antarctic circumpolar circulation to wind stress variability is studied in a simple model of the Southern Ocean. The model consists of a zonally reentrant channel with mid-ocean barrier, forced by surface heat flux and stochastic wind stress. The MITgcm code is used to solve for temperature, sea level, and the velocity field.The...

This study addresses the energetics of the Southern Ocean, in response to high-frequency wind forcing. A constant-density, multi-layer model is forced with a band of stochastically varying wind stress. The focus is on the interplay between the surface layer and the interior circulation. In line with previous examinations, it is concluded that the i...

This study addresses the response of the Southern Ocean to high-frequency wind forcing, focusing on the impact of several barotropic modes on the circumpolar transport. A suite of experiments is performed with an unstratified model of the Southern Ocean, forced with a stochastic wind stress that contains a large range of frequencies with synoptic t...

A study of the stability of the global ocean circulation is performed within a coarse-resolution general circulation model. Using techniques of numerical bifurcation theory, steady states of the global ocean circulation are explicitly calculated as parameters are varied. Under a freshwater flux forcing that is diagnosed from a reference circulation...

The Southern Ocean displays variability on many spatial and temporal scales, the sources of which are not always clear. For example, many studies have addressed the relation between Drake Passage transport variations and wind stress variability, but the complexity of the Southern Ocean dynamics and the sparseness of data in the region make it diffi...

ABSTRACTA systematic approach is proposed to determine thresholds in freshwater flux perturbations related to abrupt changes in the ocean's thermohaline circulation. The typical problem considered is the response of a thermohaline driven flow to a localized change, of specified strength and duration, in the surface freshwater flux. The initial tran...

A systematic approach is proposed to determine thresholds in freshwater flux perturbations related to abrupt changes in the ocean’s thermohaline circulation. The typical problem considered is the response of a thermohaline driven flow to a localized change, of specified strength and duration, in the surface freshwater flux. The initial transient re...

With the recent developments in the solution methods for large-dimensional nonlinear algebraic systems, fully-implicit ocean circulation models are now becoming feasible. In this paper, the formulation of such a three-dimensional global ocean model is presented. With this implicit model, the sensitivity of steady states to parameters can be investi...

Different equilibria of oceanic thermohaline circulation may exist under the same forcing conditions. One of the reasons for the existence of these multiple equilibria is a feedback between the overturning circulation and the advective transport of salt and heat. In an equatorially symmetric configuration, the multiple equilibria arise through symm...