Mode water ventilation and subtropical countercurrent over the North Pacific in CMIP5 simulations and future projections

Xu, Lixiao; Xie, Shang‐Ping; Liu, Qinyu

doi:10.1029/2012jc008377

Cited by 31 publications

(26 citation statements)

References 45 publications

(48 reference statements)

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“…In noneddy-resolving models, isopycnal PV dissipates too slowly along the low-PV tongues of the core layers of STMW and CMW. Such nonconservative properties of mode water PV in observations and eddy-resolving models have important implications in regard to their effects on the North Pacific subtropical countercurrent [Kubokawa, 1997;Kobashi et al, 2006;Xu et al, 2012b] and ocean stratification in general. Dissipation of mode waters and the effects of eddies are important subjects of future studies.…”

Section: 1002/2014jc009861mentioning

confidence: 99%

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Mesoscale eddy effects on the subduction of North Pacific mode waters

Xie

McClean

et al. 2014

JGR Oceans

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Mesoscale eddy effects on the subduction of North Pacific mode waters are investigated by comparing observations and ocean general circulation models where eddies are either parameterized or resolved. The eddy-resolving models produce results closer to observations than the noneddy-resolving model. There are large discrepancies in subduction patterns between eddy-resolving and noneddy-resolving models. In the noneddy-resolving model, subduction on a given isopycnal is limited to the cross point between the mixed layer depth (MLD) front and the outcrop line whereas in eddy-resolving models and observations, subduction takes place in a broader, zonally elongated band within the deep mixed layer region. Mesoscale eddies significantly enhance the total subduction rate, helping create remarkable peaks in the volume histogram that correspond to North Pacific subtropical mode water (STMW) and central mode water (CMW). Eddy-enhanced subduction preferentially occurs south of the winter mean outcrop. With an anticyclonic eddy to the west and a cyclonic eddy to the east, the outcrop line meanders south, and the thermocline/MLD shoals eastward. As eddies propagate westward, the MLD shoals, shielding the water of low potential vorticity from the atmosphere. The southward eddy flow then carries the subducted water mass into the thermocline. The eddy subduction processes revealed here have important implications for designing field observations and improving models.

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Section: 1002/2014jc009861mentioning

confidence: 99%

“…A bias common to climate models in the North Pacific is that they simulate too much mode water [Ladd and Thompson, 2001;Xie et al, 2011;Xu et al, 2012aXu et al, , 2012b. The potential vorticity (PV) minimum on isopycnals, a standard identifier of mode water, is too low in climate models relative to observational estimates.…”

Section: Introductionmentioning

confidence: 99%

Mesoscale eddy effects on the subduction of North Pacific mode waters

Xie

McClean

et al. 2014

JGR Oceans

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“…The surface recirculation can be strengthened with increased stratification (Sun et al 2013). The change in the surface heat flux can reduce the amount of the central mode water (Xu et al 2012) and can further enhance the heat content in the recirculation gyre by decreasing the mode water thickness (Luo et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Robust Warming Pattern of Global Subtropical Oceans and Its Mechanism

et al. 2015

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The subsurface ocean response to anthropogenic climate forcing remains poorly characterized. From the Coupled Model Intercomparison Project (CMIP), a robust response of the lower thermocline is identified, where the warming is considerably weaker in the subtropics than in the tropics and high latitudes. The lower thermocline change is inversely proportional to the thermocline depth in the present climatology. Ocean general circulation model (OGCM) experiments show that sea surface warming is the dominant forcing for the subtropical gyre change in contrast to natural variability for which wind dominates, and the ocean response is insensitive to the spatial pattern of surface warming. An analysis based on a ventilated thermocline model shows that the pattern of the lower thermocline change can be interpreted in terms of the dynamic response to the strengthened stratification and downward heat mixing. Consequently, the subtropical gyres become intensified at the surface but weakened in the lower thermcline, consistent with results from CMIP experiments.

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“…Warmer, more stratified oceans and a poleward expansion of such regions are robust consequences of increased greenhouse gas forcing (e.g., Xu et al, 2012). Four of the six models have DNF occurring primarily in this type of environments (Figure 1).…”

Section: What Are the Implications Of Cmip5 Results For Dnf And Primamentioning

confidence: 99%

“…The lack of observations in the eastern boundary current waters and the generally weak spatial correlation between models and observations prevents any firm statement that one or the other group of models is more realistic. However, the limited metrics available suggest that GFDL and MPI are as skillful as any of the others, despite the bias in the distribution of observations towards habitats that the other group assumes are most important.Warmer, more stratified oceans and a poleward expansion of such regions are robust consequences of increased greenhouse gas forcing (e.g., Xu et al, 2012). Four of the six models have DNF occurring primarily in this type of environments (Figure 1).…”

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Ocean dinitrogen fixation and its potential effects on ocean primary production in Earth system model simulations of anthropogenic warming

Riche

Christian

2018

Elementa: Science of the Anthropocene

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Dinitrogen fixation (DNF) provides a large fraction of the 'new' nitrogen supporting upper ocean productivity, and is associated with environmental conditions likely to show substantial change under anthropogenic warming. For example, surface warming induces stronger stratification, weaker nutrient supply and more rapid nutrient depletion. Using six Earth System Models, we have examined spatial patterns and trends of DNF in the CMIP5 historical and RCP 8.5 experiments. Four models (CanESM2, CESM1-BGC, IPSL-CM5R-LR, and UVicESCM) show high DNF rates in warm, stratified waters mostly associated with the western parts of the ocean basins, while GFDL-ESM2M and MPI-ESM-LR show elevated rates near the eastern boundaries because of coupling of DNF and denitrification. Despite a growing body of data, the spatial pattern of DNF is still insufficiently resolved by available observations, and none of the models agrees well with the observations. Modelled and observed rates are mostly in the same general range except for UVicESCM, and frequency distributions are similar, but spatial pattern correlations are weak and in most cases not statistically significant. Only a few models show strong trends in DNF and primary production in a warming climate, and the signs of the trends are inconsistent. Observations of primary production at the benchmark subtropical station ALOHA (22.75°N, 158°W) and proxies for historical DNF from the same region appear to corroborate trends in CanESM2 that are not present in other models. However, the CanESM DNF parameterization does not include any limitation by P or Fe, so modelled future trends may not materialize due to nutrient limitation. Analysis of available models and observations suggests that our understanding of environmental controls on ocean DNF remains limited and future trends are highly uncertain. Long-term global simulations of DNF will only be meaningful if we maintain long-term observations and extend coverage to undersampled regions.Keywords: ocean dinitrogen fixation; Earth system modelling; anthropogenic climate change Riche and Christian: Ocean dinitrogen fixation and its potential effects on ocean primary production in Earth system model simulations of anthropogenic warming Art. 16, page 2 of 18 of phosphorus or iron are available, with opposing effects on primary production (Karl et al., 1995(Karl et al., , 1997Karl, 1999). As diazotrophic phytoplankton thrive in warm, stratified waters (Sohm et al., 2011), investigating the potentially enhanced role of diazotrophs in tropical and subtropical ocean ecosystems in a warming climate is important. Proxy δ 15N measurements of the DNF contribution to the N inventory in the subtropical Pacific suggest that the recent apparent enhancement discussed by Karl (1999) is a long-term trend throughout the 20 th century, possibly associated with anthropogenic warming (Sherwood et al., 2014).We have examined trends in DNF in a variety of Earth System Models associated with the CMIP5 project (Taylor et al., 2012) to determine which if any sh...

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Mode water ventilation and subtropical countercurrent over the North Pacific in CMIP5 simulations and future projections

Cited by 31 publications

References 45 publications

Mesoscale eddy effects on the subduction of North Pacific mode waters

Mesoscale eddy effects on the subduction of North Pacific mode waters

Robust Warming Pattern of Global Subtropical Oceans and Its Mechanism

Ocean dinitrogen fixation and its potential effects on ocean primary production in Earth system model simulations of anthropogenic warming

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