New Record Ocean Temperatures and Related Climate Indicators in 2023

The global physical and biogeochemical environment has been substantially altered in response to increased atmospheric greenhouse gases from human activities.In 2023,the sea surface temperature(SST)and upper 2000 m ocean heat content(OHC)reached record highs.The 0–2000 m OHC in 2023 exceeded that of 2022 by 15±10 ZJ(1 Zetta Joules=1021 Joules)(updated IAP/CAS data);9±5 ZJ(NCEI/NOAA data).The Tropical Atlantic Ocean,the Mediterranean Sea,and southern oceans recorded their highest OHC observed since the 1950s.Associated with the onset of a strong El Niño,the global SST reached its record high in 2023 with an annual mean of~0.23℃ higher than 2022 and an astounding>0.3℃ above 2022 values for the second half of 2023.The density stratification and spatial temperature inhomogeneity indexes reached their highest values in 2023.

Another Year of Record Heat for the Oceans

Changes in ocean heat content(OHC), salinity, and stratification provide critical indicators for changes in Earth’s energy and water cycles. These cycles have been profoundly altered due to the emission of greenhouse gasses and other anthropogenic substances by human activities, driving pervasive changes in Earth’s climate system. In 2022, the world’s oceans, as given by OHC, were again the hottest in the historical record and exceeded the previous 2021 record maximum.According to IAP/CAS data, the 0–2000 m OHC in 2022 exceeded that of 2021 by 10.9 ± 8.3 ZJ(1 Zetta Joules = 1021Joules);and according to NCEI/NOAA data, by 9.1 ± 8.7 ZJ. Among seven regions, four basins(the North Pacific, North Atlantic, the Mediterranean Sea, and southern oceans) recorded their highest OHC since the 1950s. The salinity-contrast index, a quantification of the “salty gets saltier–fresh gets fresher” pattern, also reached its highest level on record in 2022,implying continued amplification of the global hydrological cycle. Regional OHC and salinity changes in 2022 were dominated by a strong La Ni?a event. Global upper-ocean stratification continued its increasing trend and was among the top seven in 2022.

Three-dimensional properties of mesoscale cyclonic warm-core and anticyclonic cold-core eddies in the South China Sea

In general,a mesoscale cyclonic(anticyclonic)eddy has a colder(warmer)core,and it is considered as a cold(warm)eddy.However,recently research found that there are a number of"abnormal"mesoscale cyclonic(anticyclonic)eddies associated with warm(cold)cores in the South China Sea(SCS).These"abnormal"eddies pose a challenge to previous works on eddy detection,characteristic analysis,eddy-induced heat and salt transports,and even on mesoscale eddy dynamics.Based on a 9-year(2000–2008)numerical modelling data,the cyclonic warm-core eddies(CWEs)and anticyclonic cold-core eddies(ACEs)in the SCS are analyzed.This study found that the highest incidence area of the"abnormal"eddies is the northwest of Luzon Strait.In terms of the eddy snapshot counting method,8620 CWEs and 9879 ACEs are detected,accounting for 14.6%and 15.8%of the total eddy number,respectively.The size of the"abnormal"eddies is usually smaller than that of the"normal"eddies,with the radius only around 50 km.In the generation time aspect,they usually appear within the 0.1–0.3 interval in the normalized eddy lifespan.The survival time of CWEs(ACEs)occupies 16.3%(17.1%)of the total eddy lifespan.Based on two case studies,the intrusion of Kuroshio warm water is considered as a key mechanism for the generation of these"abnormal"eddies near the northeastern SCS.

Another Record: Ocean Warming Continues through 2021 despite La Nina Conditions

The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content(OHC). Here, we provide the first analysis of recent OHC changes through 2021 from two international groups. The world ocean, in 2021, was the hottest ever recorded by humans, and the 2021 annual OHC value is even higher than last year’s record value by 14 ± 11 ZJ(1 zetta J = 1021 J) using the IAP/CAS dataset and by16 ± 10 ZJ using NCEI/NOAA dataset. The long-term ocean warming is larger in the Atlantic and Southern Oceans than in other regions and is mainly attributed, via climate model simulations, to an increase in anthropogenic greenhouse gas concentrations. The year-to-year variation of OHC is primarily tied to the El Nino-Southern Oscillation(ENSO). In the seven maritime domains of the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern oceans,and the Mediterranean Sea, robust warming is observed but with distinct inter-annual to decadal variability. Four out of seven domains showed record-high heat content in 2021. The anomalous global and regional ocean warming established in this study should be incorporated into climate risk assessments, adaptation, and mitigation.

Upper Ocean Temperatures Hit Record High in 2020

The long-term warming of the ocean is a critical indicator of both the past and present state of the climate system. It also provides insights about the changes to come, owing to the persistence of both decadal variations and secular trends,which the ocean records extremely well(Hansen et al., 2011;IPCC, 2013;Rhein et al., 2013;Trenberth et al., 2016;Abram et al., 2019).

Intraseasonal variability of the surface zonal current in the equatorial Indian Ocean:Seasonal differences and causes

Using observations and numerical simulations,this study examines the intraseasonal variability of the surface zonal current(u ISV)over the equatorial Indian Ocean,highlighting the seasonal and spatial differences,and the causes of the differences.Large-amplitude u ISV occurs in the eastern basin at around 80°–90°E and near the western boundary at 45°–55°E.In the eastern basin,the u ISV is mainly caused by the atmospheric intraseasonal oscillations(ISOs),which explains 91%of the standard deviation of the total u ISV.Further analysis suggests that it takes less than ten days for the intraseasonal zonal wind stress to generate the u ISV through the directly forced Kelvin and Rossby waves.Driven by the stronger zonal wind stress associated with the Indian summer monsoon ISO(MISO),the eastern u ISV in boreal summer(May to October)is about 1.5 times larger than that in boreal winter(November to April).In the western basin,both the atmospheric ISOs and the oceanic internal instabilities contribute substantially to the u ISV,and induce stronger u ISV in boreal summer.Energy budget analysis suggests that the mean flow converts energy to the intraseasonal current mainly through barotropic instabilities.

Four-channel CWDM transmitter chip based on thin-film lithium niobate platform

Multi-lane integrated transmitter chips are key components in future compact optical modules to realize high-speed optical interconnects.Thin-film lithium niobate(TFLN)photonics have emerged as a promising platform for achieving high-performance chip-scale optical systems.Combining a coarse wavelength-division multiplexing(CWDM)devices using fabrication-tolerant angled multimode interferometer structure and high-performance electro-optical modulators,we demonstrate monolithic on-chip four-channel CWDM transmitter on the TFLN platform for the first time.The four-channel CWDM transmitter enables high-speed transmissions of 100 Gb/s data rate per wavelength channel(i.e.,an aggregated date rate of 400 Gb/s).

Three-dimensional characteristics of mesoscale eddies simulated by a regional model in the northwestern Pacific Ocean during 2000–2008

Mesoscale eddies play vital roles in ocean processes.Although previous studies focused on eddy surface features and individual three-dimensional(3D)eddy cases in the northwestern Pacific Ocean,the analysis of unique eddy3D regional characteristics is still lacking.A 3D eddy detection scheme is applied to 9 years(2000-2008)of eddyresolving Regional Ocean Modeling System(ROMS)output to obtain a 3D eddy dataset from the surface to a depth of 1000 m in the northwestern Pacific Ocean(15°-35°N,120°-145°E).The 3D characteristics of mesoscale eddies are analyzed in two regions,namely,Box1(Subtropical Countercurrent,15°-25°N,120°-145°E)and Box2(Southern Kuroshio Extension,25°-35°N,120°-145°E).In Box1,the current is characterized by strong vertical shear and weak horizontal shear.In Box2,the current is characterized by the strong Kuroshio,topographic effect,and the westward propagation of Rossby waves.The results indicate the importance of baroclinic instability in Box1,whereas in Box2,both the barotropic and baroclinic instability are important.Moreover,the mesoscale eddies’properties in Box1 and Box2 are distinct.The eddies in Box1 have larger number and radius but a shorter lifetime.By contrast,Box2 has fewer eddies,which have smaller radius but longer lifetime.Vertically,more eddies are detected at the subsurface than at the surface in both regions;the depth of 650 m is the turning point in Box1.Above this depth,the number of cyclonic eddies(CEs)is larger than that of anticyclonic eddies(AEs).In Box2,the number of CEs is dominant vertically.Eddy kinetic energy(EKE)and mean normalized relative vorticity in Box2are significantly higher than those in Box1.With increasing depth,the attenuation trend of EKE and relative vorticity of Box1 become greater than those of Box2.Furthermore,the upper ocean(about 300 m in depth)contains 68.6%of the eddies(instantaneous eddy).Only 16.6%of the eddies extend to 1000 m.In addition,about87%of the eddies are bowl-shaped eddies in the two regions.Only about 3%are cone-shaped eddies.With increasing depth of the eddies,the proportion of bowl-shaped eddies gradually decreases.Conversely,the coneand lens-shaped eddies are equal in number at 700-1000 m,accounting for about 30%each.Studying the 3D characteristics of eddies in two different regions of the northwestern Pacific Ocean is an important stepping stone for discussing the different eddy generation mechanisms.

Effect of seasonal barrier layer on mixed-layer heat budget in the Bay of Bengal

Time series measurements (2010–2017) from the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) moorings at 15°N,90°E and 12°N,90°E are used to investigate the effect of the seasonal barrier layer (BL) on the mixed-layer heat budget in the Bay of Bengal (BoB).The mixed-layer temperature tendency (?T/?t) is primarily controlled by the net surface heat flux that remains in the mixed layer(Q’) from March to October,while both Q’and the vertical heat flux at the base of the mixed layer (Q_(h)),estimated as the residual of the mixed-layer heat budget,dominate during winter (November–February).An inverse relation is observed between the BL thickness and the mixed-layer temperature (MLT).Based on the estimations at the moorings,it is suggested that when the BL thickness is≥25 m,it exerts a considerable influence on ?T/?t through the modulation of Q_(h) (warming) in the BoB.The cooling associated with Q_(h) is strongest when the BL thickness is≤10 m with the MLT exceeding 29°C,while the contribution from Q_(h) remains nearly zero when the BL thickness varies between 10 m and 25 m.Temperature inversion is evident in the BoB during winter when the BL thickness remains≥25 m with an average MLT<28.5°C.Furthermore,Q_(h) follows the seasonal cycle of the BL at these RAMA mooring locations,with r>0.72 at the 95%significance level.

Ultra-high extinction ratio optical pulse generation with a thin film lithium niobate modulator for distributed acoustic sensing

We experimentally demonstrate ultra-high extinction ratio(ER)optical pulse modulation with an electro-optical modulator(EOM)on thin film lithium niobate(TFLN)and its application for fiber optic distributed acoustic sensing(DAS).An interface carrier effect leading to a relaxation-tail response of TFLN EOM is discovered,which can be well addressed by a small compensation component following the main driving signal.An ultrahigh ER>50 dB is achieved by canceling out the tailed response during pulse modulation using the EOM based on a cascaded Mach–Zehnder interferometer(MZI)structure.The modulated optical_(√)pulses are then utilized as a probe light for a DAS system,showing a sensitivity up to-62.9 dB·rad∕Hz~2(7 pε/Hz)for 2-km single-mode sensing fiber.Spatial crosstalk suppression of 24.9 dB along the fiber is also obtained when the ER is improved from 20 dB to 50 dB,clearly revealing its importance to the sensing performance.

Robust thin-film lithium niobate modulator on a silicon substrate with backside holes

Recently,Mach–Zehnder modulators based on thin-film lithium niobate have attracted broad interest for their potential for high modulation bandwidth,low insertion loss,high extinction ratio,and high modulation efficiency.The periodic capacitively loaded traveling-wave electrode is optimally adopted for ultimate high-performances in this type of modulator.However,such an electrode structure on a silicon substrate still suffers from the velocity mismatch and substrate leakage loss for microwave signals.Here,we introduce a thin-film lithium niobate modulator structure using this periodic capacitively loaded electrode on a silicon substrate.Backside holes in the silicon substrate are prepared to solve robustly the above difficulties.The fabricated device exhibits an insertion loss of 0.9 dB,a halfwave-voltage–length product of 2.18 V·cm,and an ultra-wide bandwidth well exceeding 67 GHz for a 10-mm-long device.Data transmissions with rates up to 112 Gb/s are demonstrated.The proposed structure and fabrication strategy are compatible for other types of monolithic and heterogeneous integrated thin-film lithium niobate modulators on a silicon substrate.

Anisotropy-free arrayed waveguide gratings on X-cut thin film lithium niobate platform of in-plane anisotropy

Arrayed waveguide grating is a versatile and scalable integrated light dispersion device,which has been widely adopted in various applications,including,optical communications and optical sensing.Recently,thin-film lithium niobate emerges as a promising photonic integration platform,due to its ability of shrinking largely the size of typical lithium niobate based optical devices.This would also enable multifunctional photonic integrated chips on a single lithium niobate substrate.However,due to the intrinsic anisotropy of the material,to build an arrayed waveguide grating on X-cut thin-film lithium niobate has never been successful.Here,a universal strategy to design anisotropyfree dispersive components on a uniaxial in-plane anisotropic photonic integration platform is introduced for the first time.This leads to the first implementation of arrayed waveguide gratings on X-cut thin-film lithium niobate with various configurations and high-performances.The best insertion loss of 2.4 dB and crosstalk of−24.1 dB is obtained for the fabricated arrayed waveguide grating devices.Applications of such arrayed waveguide gratings as a wavelength router and in a wavelength-division multiplexed optical transmission system are also demonstrated.

Four-channel CWDM device on a thin-film lithium niobate platform using an angled multimode interferometer structure

A compact and high-performance coarse wavelength-division multiplexing(CWDM) device is introduced with a footprint of 2.1 mm × 0.02 mm using an angled multimode interferometer structure based on a thin-film lithium niobate(TFLN) platform.The demonstrated device built on a 400 nm thick x-cut TFLN shows ultra-low insertion losses of <0.72 dB.Measured 3 dB bandwidths are 12.1 nm for all channels,and cross talks from adjacent channels are better than 18 dB.Its peak wavelength positions comply with the CWDM standard with a channel spacing of 20 nm.The filter bandwidth of the proposed CWDM device can be tuned by adjusting the structural parameters.This demonstrated CWDM device will promote future realization of multi-channel and multi-wavelength transmitter chips on TFLN.

Multi-scale variability of the tropical Indian Ocean circulation system revealed by recent observations

The tropical Indian Ocean circulation system includes the equatorial and near-equatorial circulations, the marginal sea circulation, and eddies. The dynamic processes of these circulation systems show significant multi-scale variability associated with the Indian Monsoon and the Indian Ocean dipole. This paper summarizes the research progress over recent years on the tropical Indian Ocean circulation system based on the large-scale hydrological observations and numerical simulations by the South China Sea Institute of Oceanology(SCSIO), Chinese Academy of Sciences. Results show that:(1) the wind-driven Kelvin and Rossby waves and eastern boundary-reflected Rossby waves regulate the formation and evolution of the Equatorial Undercurrent and the Equatorial Intermediate Current;(2) the equatorial wind-driven dynamics are the main factor controlling the inter-annual variability of the thermocline in the eastern Indian Ocean upwelling;(3) the equatorial waves transport large amounts of energy into the Bay of Bengal in forms of coastal Kelvin and reflected free Rossby waves. Several unresolved issues within the tropical Indian Ocean are discussed:(i) the potential effects of the momentum balance and the basin resonance on the variability of the equatorial circulation system, and(ii) the potential contribution of wind-driven dynamics to the life cycle of the eastern Indian Ocean upwelling. This paper also briefly introduces the international Indian Ocean investigation project of the SCSIO, which will advance the study of the multi-scale variability of the tropical Indian Ocean circulation system, and provide a theoretical and data basis to support marine environmental security for the countries around the Maritime Silk Road.

Accelerated spread of Fukushima’s waste water by ocean circulation

Japan announced that the treated waste water contaminated by the wrecked Fukushima Daiichi Nuclear Power Plant will be released to the Pacific Ocean.Since the waste water still contains tritium and trace amounts of other radionuclides,the decision immediately raises many general concerns for people,especially residents of neighboring countries,and has been condemned by environmental groups and fisheries organizations.