Reproductive Biology of Yellowfin Tuna T. albacares in the West-Central Indian Ocean

Survey of yellowfin tuna in the west-central Indian Ocean was conducted on board of Chinese longliners during 2003,2004 and 2005,which is a part of Chinese Tuna Fishery Scientific Observer Program(CTFSOP) . The reproductive biology has been investigated. A total of 1 023 samples are collected including 417 ovaries and 606 testes. Spawning activities of yellowfin tuna have been studied for both male and female from January to June. The data showed that the average monthly sex ratio is 0.59,and the minimum length at sexual maturity is 101 cm for female and 110 cm for male respectively. Length at 50% sexual maturity is esti-mated at 113.77 cm for female and 120.20 cm for male,whereas maturation rate is 0.066 cm-1 for female and 0.091 cm-1 for male. Sex ratio by length class indicates that the proportion of male is higher than female's along with size increasing;for instance,in the group of the body length longer than 145 cm,some females have their body length from 145 to 160 cm and males have their body length at 160 cm and even longer. Statistically,yellowfin tuna has a significant seasonal reproduction.

Characteristics and triggering mechanisms of early negative Indian Ocean Dipole

Negative Indian Ocean Dipole(nIOD)can exert great impacts on global climate and can also strongly influence the climate in China.Early nIOD is a major type of nIOD,which can induce more pronounced climate anomalies in summer than La Niña-related nIOD.However,the characteristics and triggering mechanisms of early nIOD are unclear.Our results based on reanalysis datasets indicate that the early nIOD and La Niña-related nIOD are the two major types of nIOD,and the former accounts for over one third of all the nIOD events in the past six decades.These two types of nIODs are similar in their intensities,but are different in their spatial patterns and seasonal cycles.The early nIOD,which develops in spring and peaks in summer,is one season earlier than the La Niña-related nIOD.The spatial pattern of the wind anomaly associated with early nIOD exhibits a winter monsoon-like pattern,with strong westerly anomalies in the equatorial Indian Ocean and eastly anomalies in the northern Indian Ocean.Opposite to the triggering mechanism of early positve IOD,the early nIOD is induced by delayed Indian summer monsoon onset.The results of this study are helpful for improving the prediction skill of IOD and its climate impacts.

Deep learning to estimate ocean subsurface salinity structure in the Indian Ocean using satellite observations

Accurately estimating the ocean subsurface salinity structure(OSSS)is crucial for understanding ocean dynamics and predicting climate variations.We present a convolutional neural network(CNN)model to estimate the OSSS in the Indian Ocean using satellite data and Argo observations.We evaluated the performance of the CNN model in terms of its vertical and spatial distribution,as well as seasonal variation of OSSS estimation.Results demonstrate that the CNN model accurately estimates the most significant salinity features in the Indian Ocean using sea surface data with no significant differences from Argo-derived OSSS.However,the estimation accuracy of the CNN model varies with depth,with the most challenging depth being approximately 70 m,corresponding to the halocline layer.Validations of the CNN model’s accuracy in estimating OSSS in the Indian Ocean are also conducted by comparing Argo observations and CNN model estimations along two selected sections and four selected boxes.The results show that the CNN model effectively captures the seasonal variability of salinity,demonstrating its high performance in salinity estimation using sea surface data.Our analysis reveals that sea surface salinity has the strongest correlation with OSSS in shallow layers,while sea surface height anomaly plays a more significant role in deeper layers.These preliminary results provide valuable insights into the feasibility of estimating OSSS using satellite observations and have implications for studying upper ocean dynamics using machine learning techniques.

Circulation Patterns Linked to the Positive Sub-Tropical Indian Ocean Dipole

The positive phase of the subtropical Indian Ocean dipole(SIOD)is one of the climatic modes in the subtropical southern Indian Ocean that influences the austral summer inter-annual rainfall variability in parts of southern Africa.This paper examines austral summer rain-bearing circulation types(CTs)in Africa south of the equator that are related to the positive SIOD and the dynamics through which specific rainfall regions in southern Africa can be influenced by this relationship.Four austral summer rain-bearing CTs were obtained.Among the four CTs,the CT that featured(i)enhanced cyclonic activity in the southwest Indian Ocean;(ii)positive widespread rainfall anomaly in the southwest Indian Ocean;and(iii)low-level convergence of moisture fluxes from the tropical South Atlantic Ocean,tropical Indian Ocean,and the southwest Indian Ocean,over the south-central landmass of Africa,was found to be related to the positive SIOD climatic mode.The relationship also implies that positive SIOD can be expected to increase the amplitude and frequency of occurrence of the aforementioned CT.The linkage between the CT related to the positive SIOD and austral summer homogeneous regions of rainfall anomalies in Africa south of the equator showed that it is the principal CT that is related to the inter-annual rainfall variability of the south-central regions of Africa,where the SIOD is already known to significantly influence its rainfall variability.Hence,through the large-scale patterns of atmospheric circulation associated with the CT,the SIOD can influence the spatial distribution and intensity of rainfall over the preferred landmass through enhanced moisture convergence.

The Relationship Between Indian Ocean SST and Tropical Cyclone Genesis Frequency over North Indian Ocean in May

Tropical cyclone(TC)activities in the North Indian Ocean(NIO)peak in May during the pre-monsoon period,but the TC frequency shows obvious inter-annual variations.By conducting statistical analysis and dynamic diagnosis of long-term data from 1948 to 2016,the relationship between the inter-annual variations of Indian Ocean SST and NIO TC genesis frequency in May is analyzed in this paper.Furthermore,the potential mechanism concerning the effect of SST anomaly on TC frequency is also investigated.The findings are as follows:1)there is a broadly consistent negative correlation between NIO TC frequency in May and SST in the Indian Ocean from March to May,with the key influencing area located in the southwestern Indian Ocean(SWIO);2)the anomalies of SST in SWIO(SWIO-SST)are closely related to a teleconnection pattern surrounding the Indian Ocean,which can significantly modulate the high-level divergence,mid-level vertical motion and other related environmental factors and ultimately influence the formation of TCs over the NIO;3)the increasing trend of SWIO-SST may play an essential role in the downward trend of NIO TC frequency over the past 69 years.

The Coordinated Influence of Indian Ocean Sea Surface Temperature and Arctic Sea Ice on Anomalous Northeast China Cold Vortex Activities with Different Paths during Late Summer

The Northeast China cold vortex(NCCV)during late summer(from July to August)is identified and classified into three types in terms of its movement path using machine learning.The relationships of the three types of NCCV intensity with atmospheric circulations in late summer,the sea surface temperature(SST),and Arctic sea ice concentration(SIC)in the preceding months,are analyzed.The sensitivity tests by the Community Atmosphere Model version 5.3(CAM5.3)are used to verify the statistical results.The results show that the coordination pattern of East Asia-Pacific(EAP)and Lake Baikal high pressure forced by SST anomalies in the North Indian Ocean dipole mode(NIOD)during the preceding April and SIC anomalies in the Nansen Basin during the preceding June results in an intensity anomaly for the first type of NCCV.While the pattern of high pressure over the Urals and Okhotsk Sea and low pressure over Lake Baikal during late summer-which is forced by SST anomalies in the South Indian Ocean dipole mode(SIOD)in the preceding June and SIC anomalies in the Barents Sea in the preceding April-causes the intensity anomaly of the second type.The third type is atypical and is not analyzed in detail.Sensitivity tests,jointly forced by the SST and SIC in the preceding period,can well reproduce the observations.In contrast,the results forced separately by the SST and SIC are poor,indicating that the NCCV during late summer is likely influenced by the coordinated effects of both SST and SIC in the preceding months.

The Subsurface and Surface Indian Ocean Dipoles and Their Association with ENSO in CMIP6 models

This study assesses the reproducibility of 31 historical simulations from 1850 to 2014 in the Coupled Model Intercomparison Project phase 6(CMIP6) for the subsurface(Sub-IOD) and surface Indian Ocean Dipole(IOD) and their association with El Ni?o-Southern Oscillation(ENSO). Most CMIP6 models can reproduce the leading east-west dipole oscillation mode of heat content anomalies in the tropical Indian Ocean(TIO) but largely overestimate the amplitude and the dominant period of the Sub-IOD. Associated with the much steeper west-to-east thermocline tilt of the TIO, the vertical coupling between the Sub-IOD and IOD is overly strong in most CMIP6 models compared to that in the Ocean Reanalysis System 4(ORAS4). Related to this, most models also show a much tighter association of Sub-IOD and IOD events with the canonical ENSO than observations. This explains the more(less) regular Sub-IOD and IOD events in autumn in those models with stronger(weaker) surface-subsurface coupling in TIO. Though all model simulations feature a consistently low bias regarding the percentage of the winter–spring Sub-IOD events co-occurring with a Central Pacific(CP) ENSO, the linkage between a westward-centered CP-ENSO and the Sub-IOD that occurs in winter–spring, independent of the IOD, is well reproduced.

Assessment of Sea Surface Temperature Warming in the Tropical Indian Ocean Simulated by CMIP Models

The tropical Indian Ocean is an important region that affects local and remote climate systems,and the simulation of longterm trends in sea surface temperature(SST)is a major focus of climate research.This study presents a preliminary assessment of multiple model simulations of tropical Indian Ocean SST warming from 1950 to 1999 based on outputs from the 20 Coupled Model Intercomparison Project(CMIP)Phase 5(CMIP5)models and the 36 CMIP 6(CMIP6)models to analyze and compare the warming patterns in historical simulations.Results indicate large discrepancies in the simulations of tropical Indian Ocean SST warming,especially for the eastern equatorial Indian Ocean.The multimodel ensemble mean and most of the individual models generally perform well in reproducing basin-wide SST warming.However,the strength of the SST warming trends simulated by the CMIP5 and CMIP6 models are weaker than those observed,especially for the CMIP6 models.In addition to the general warming trend analysis,decadal trends are also assessed,and a statistical method is introduced to measure the near-term variability in an SST time series.The simulations indicate large decadal variability over the entire tropical Indian Ocean,differing from observations in which significant decadal trend variability is observed only in the southeastern Indian Ocean.In the CMIP model simulations,maximum decadal variability occurs in boreal autumn,but the observations display the minimum and maximum variability in boreal autumn and spring,respectively.

Assessment of Atmospheric Reanalysis Data Based on Buoy Observations over the Tropical Western Indian Ocean in 2019

Atmospheric reanalysis data are an important data source for studying weather and climate systems.The sea surface wind and sea level pressure observations measured from a real-time buoy system deployed in Kenya’s offshore area in 2019 conducted jointly by Chinese and Kenyan scientists were used to evaluate the performance of the major high-frequency atmospheric reanalysis products in the western Indian Ocean region.Compared with observations,the sea level pressure field could be accurately simulated using the atmospheric reanalysis data.However,significant discrepancies existed between the surface wind reanalysis data,especially between meridional wind and the observational data.Most of the data provide a complete understanding of sea level pressure,except for the Japanese 55-year Reanalysis data,which hold a significant system bias.The Modern-Era Reanalysis for Research and Applications,Version-2,provides an improved description of all datasets.All the reanalysis datasets for zonal wind underestimate the strength during the study period.Among reanalysis data,NCEP-DOE Atmospheric Model Intercomparison Project reanalysis data presents an inaccurate description due to the worst correlation with the observations.For meridional wind,most reanalysis datasets underestimate the variance,while the European Centre for Medium-Range Weather Forecasts Atmospheric Composition Reanalysis 4 has a larger variance than the observations.In addition to the original data comparison,the diurnal variability of sea level pressure and surface wind are also assessed,and the result indicates that the diurnal variations have a significant gap between observation and reanalysis data.This study indicates that the current high-frequency reanalysis data still have disadvantages when describing the atmospheric parameters in the Western Indian Ocean region.

Spatial Distribution and Seasonal Variation of Hypoxic Zone in the Eastern Equatorial Indian Ocean

The spatial distribution and seasonal variations of the hypoxic zone in the eastern equatorial Indian Ocean were investigated using survey data collected from four cruises from 2013 to 2018.Results showed that hypoxic zone occurred all year round in the eastern equatorial Indian Ocean,and it spread southward in the shape of a double tongue at two depths with one at subsurface centered at a depth of 150 m and the other in intermediate water centered at a depth of 800 m.The southward expansion and maximum thickness of the hypoxic zone were greatest in the spring inter-monsoon and least in the summer monsoon.The hypoxic zone originated from the southward expansion of the hypoxic water in the Bay of Bengal and its spatial distribution was driven by southward output flux of mid-deep(100–1000 m)hypoxic water from the Bay of Bengal.The hypoxia southward expansion was blocked near the equator in the subsurface layer,because of mixing with multiple zonal circulations(e.g.,Wyrtki Jets and the equatorial undercurrent),which meant that the hypoxic zone extended over a smaller area than in the intermediate water.These new findings will contribute to an improved understanding of the hypoxic zone and will contribute to circulation research,particularly about intermediate circulation in the eastern equatorial Indian Ocean.

The Origin and Preservation of Suspended Barites near the 90°E Ridge in the Northeastern Indian Ocean

Suspended particulate barite crystals were detected in the water columns at four different stations near the 90°E ridge in the Indian Ocean.Four distinct morphological types of marine barites were distinguished:euhedral-subhedral crystals,oval or round crystals,rhombic crystals,and irregular crystals.The barite crystals in the study area are typically fine,with a dominant size of 1–3μm.The vertical distribution of barites is significantly affected by the formation and sedimentation processes.Barites begin to appear at a depth of 30 m and are formed primarily from the surface to the depth of 2000m with a concentration peak at the depth of 200m,where particles are coarser than those in the other layers.The barites begin to settle and dissolve once formed in the water column,resulting in finer barite particles and lower particle concentrations.The formation of barite crystals is related to biological processes associated with the decomposition of barium-rich skeletons in the microenvironment of decaying organic matter that is affected by the primary productivity and dissolved oxygen content in the water column.The dissolving process of barite crystals showed similar variation with the concentration of dissolved barium in ocean water,and the substitution of strontium for barite in crystals promotes the selective dissolution of barite and exerts an important impact on its morphology.It is approximately 33%of barites in the amount and 22%in the concentration to settle to the bottom of the water column compared to that observed in the main barite formation zone.

Mixed layer warming by the barrier layer in the southeastern Indian Ocean

The southeastern Indian Ocean is characterized by the warm barrier layer(BL)underlying the cool mixed layer water in austral winter.This phenomenon lasts almost half a year and thus provides a unique positive effect on the upper mixed layer heat content through the entrainment processes at the base of the mixed layer,which has not been well evaluated due to the lack of proper method and dataset.Among various traditional threshold methods,here it is shown that the 5 m fixed depth difference can produce a reliable and accurate estimate of the entrainment heat flux(EHF)in this BL region.The comparison between the daily and monthly EHF warming indicates that the account for high-frequency EHF variability almost doubles the warming effect in the BL period,which can compensate for or even surpass the surface heat loss.This increased warming is a result of stronger relative rate of the mixed layer deepening and larger temperature differences between the mixed layer and its immediate below in the daily-resolving data.The interannual EHF shows a moderately increasing trend and similar variabilities to the Southern Annular Mode(SAM),likely because the mixed layer deepening under the positive SAM trend is accompanied by enhanced turbulent entrainment and thus increases the BL warming.

Microplastic in the Marine Environment of the Indian Ocean

Microplastic has been found in all major waterbodies in the world. Many examples of ingestion of microplastic by marine organisms have been reported. This presence of microplastic in marine organisms gives it the possibility to penetrate the human food chain by increasing the chance of microplastic in seafood targeted for human consumption. Although it is known that parts of the Indian Ocean suffer from significant plastic pollution, much of the systematic research on the microplastic abundance in different regions of the Indian Ocean stems only from the last five years. This manuscript reviews the available literature of 2015-2022 on the presence of microplastics in commercially important fish species in the Indian Ocean. The literature data on microplastic content on beaches, in subtidal sediment, in the sediment from the ocean floor, and in surface water of different regions of the Indian Ocean is reviewed, also.

Seasonal Distribution of Observed Colored Dissolved Organic Matter(CDOM)in the Eastern Indian Ocean

Colored dissolved organic matter(CDOM)is a crucial constituent that affects the optical absorption properties of seawater.Owing to the relatively limited measured data on the spatial distribution characteristics of CDOM in the tropical eastern Indian Ocean,this study analyzes the optical absorption characteristics of CDOM in the southeast Indian Ocean using the data collected during four seasons from 2013 to 2017.This work also systematically describes the seasonal horizontal and vertical distribution characteristics of CDOM in this area and conducts a preliminary analysis of the relevant factors affecting CDOM absorption characteristics in this region.Results indicate that the CDOM ag(440)during summer was remarkably lower than that in the coastal waters of Europe and coastal waters of China but slightly higher than that in the western and southeast Pacific.The spatial distribution of surface CDOM shows remarkable seasonal differences,and the spatial distribution characteristics of CDOM in the 5°S,92°E region differ between spring/summer and autumn/winter.The values of ag(400)and ag(440)are weak/strong at a surface/subsurface level of 100 m,with differences found between summer and winter.The correlation of CDOM with temperature,salinity,and chlorophyll-a concentration is relatively low,indicating that CDOM is an independent driving mechanism influenced by phytoplankton degradation,photobleaching,and water mixing.

Subthermocline eddies carrying the Indonesian Throughflow water observed in the southeastern tropical Indian Ocean

We observed a subthermocline eddy(STE)with a cold and fresh core during an observation cruise along a transect of 10°S in the southeastern tropical Indian Ocean(SETIO)in December 2017.The vertical scale,speed radius,and maximum swirl velocity of the STE were about 200 m,55 km,and 0.5 m/s,respectively.The mean Rossby number and Burger number of the STE were then estimated to be about−0.7 and 2.4,indicating the STE was a submesoscale coherent vortex.The STE core water had characteristics of the Indonesian Throughflow(ITF)water and was distinct from that of surrounding areas.By examining Argo float data,another STE was well captured by five successive profiles of the same Argo float.Both STEs showed significant temperature and salinity anomalies at theσ0=26.0-26.5 kg/m3 surfaces.With the assumption that the low-salinity ITF water parcels could be carried only by surface eddies and the STEs,the Argo profiles,which detected low-salinity ITF water and were located outside a surface eddy,were believed to be inside an STE and were used to analyze the distribution,origin,and generation mechanism of the STE.The results suggested that the STEs carrying ITF water may be generated under topography-current interaction at the eastern coastal waters or under front-induced subduction in the area away from coastal waters.Those STEs may be widely distributed in the SETIO and may play a role in ITF water parcel transport.

Revisiting the Seasonal Evolution of the Indian Ocean Dipole from the Perspective of Process-Based Decomposition

The seasonal phase-locking feature of the Indian Ocean Dipole(IOD)is well documented.However,the seasonality ten-dency of sea surface temperature anomalies(SSTAs)during the development of the IOD has not been widely investigated.The SSTA tendencies over the two centers of the IOD peak in September-October-November are of different monthly amplitudes.The SSTA tendency over the west pole is small before June-July-August but dramatically increases in July-August-September.Meanwhile,the SSTA tendency over the east pole gradually increases before June-July-August and decreases since then.The growth rate attribution of the SSTAs is achieved by examining the roles of radiative and non-radiative air-sea coupled thermodynamic processes through the climate feedback-response analysis method(CFRAM).The CFRAM results indicate that oceanic dynamic processes largely contribute to the total SSTA tendency for initiating and fueling the IOD SSTAs,similar to previous studies.However,these results cannot ex-plain the monthly amplitudes of SSTA tendency.Four negative feedback processes(cloud radiative feedback,atmospheric dynamic processes,surface sensible,and latent heat flux)together play a damping role opposite to the SSTA tendency.Nevertheless,the sea surface temperature-water vapor feedback shows positive feedback.Specifically,variations in SSTAs can change water vapor con-centrations through evaporation,resulting in anomalous longwave radiation that amplifies the initial SSTAs through positive feedback.The effect of water vapor feedback is well in-phase with the monthly amplitudes of SSTA tendency,suggesting that the water vapor feedback might modulate the seasonally dependent SSTA tendency during the development of the IOD.

Impact of Tropical Indian Ocean Temperature on the Ozone Layer in East Asia

Based on the reanalysis data of monthly mean sea surface temperature (SST) from British Hadley Center and ozone mass mixing ratio from National Aeronautics and Space Administration (NASA) during 1980-2015, two indexes IOBI and IODI of the main modes characterizing SST changes in the tropical Indian Ocean——Indian Ocean Basin (IOB) and Indian Ocean Dipole (IOD) were calculated firstly, and then the correlation of SST anomaly (SSTA) in the tropical Indian Ocean and ozone mass mixing ratio in the stratosphere over East Asia from 1980 to 2015 was analyzed. Besides, the impact of SST changes in the tropical Indian Ocean on the distribution of ozone layer in East Asia was discussed. The results show that SST changes in the tropical Indian Ocean had significant effects on stratospheric ozone distribution in East Asia, and it was consistent with the temporal changes of IOB and IOD. IOBI and IODI had a certain correlation with stratospheric ozone changes in East Asia, with a particularly significant correlation in the lower stratosphere (70 hPa) and middle stratosphere (40 hPa) especially during spring and autumn.

Impact of Southern Indian ocean dipole via the ITCZ on winter and spring precipitation in China

本文分析了1979-2021年南印度洋冬季海表面温度特征,印度洋热带辐合带(ITCZ)位置变化及其对中国冬春季降水的影响.EOF分析第一模态表明南印度洋冬季海表面温度异常显示西南-东北反相分布,即南印度洋偶极子模态(SIOD).分离厄尔尼诺-南方涛动(ENSO)信号后,纯SIOD事件对同年冬季和次年春季的印度洋ITCZ位置(35°-75°E平均)均有影响,冬季,纯正(负)SIOD事件使印度洋ITCZ往南(北)移动.春季,SIOD则使印度洋ITCZ移动方向与冬季相反,且移动幅度更大.冬,春季长江中下游地区(MLYR)的降水量与印度洋ITCZ位置分别呈正,负相关.同时,在纯正(负)SIOD事件下,冬,春季MLYR的降水分别减少,增加,可见印度洋ITCZ位置变化可能是SIOD影响MLYR冬,春季降水的媒介之一.

Microplastic pollution in the Indian Ocean: Passageways and the contamination of the open ocean and its marine environment

Microplastics(MPs)are man-made litter receiving current conversation of interest as a silent pollutant to Earth.Its impact is high on the coastal waters,sediment and organisms of the marine environment.It is a pertinent requirement to investigate the microplastic MP contamination in the marine environment of the Asian region aiming at the world’s 3rd largest ocean,the Indian Ocean.Among the different samples,Indian Ocean water and deep-sea sediment samples have mostly been investigated covering the Southwestern Sumatran region(Eastern Indian Ocean)which is a well-known domestic and industrial shipping route.Majority of the tested samples were in the form of granules,fibers and fragments of 100-500μm and 38-6,330μm in size range respectively in deep-sea sediment samples and in ocean water samples.Further,the prominent MPs types were PVC(polyvinyl chloride),PP(polypropylene)synthetic micro debris,Poly methyl methacrylate PMMA plastic micro debris,PTFE(polytetrafluoroethylene),and nylon.Floating plastic debris has also been found on surface ocean waters in the Eastern Indian Oceanic region as an emergent floating litter.Its size range and the percentage abundance were documented as 0.5-5 mm and 50%respectively.Moreover,the Western Indian Oceanic region has reported the highest percentage abundance of MPs in ocean waters(10.48%).These MPs were assumed to derive from fiber or fishing line material,regional fishery activities and the sewage disposal debris of tourist-based coastline anthropogenic activities.The polymer-specific sources that release this potential pollutant were not yet accurately discovered.This review article elaborates on the topic by reviewing the MPs’pervasiveness,identifying different passageways and sources of discharging MPs to the Indian Ocean and finally the ecological and socio economic risks of the matter.Thus,it may highlight the knowledge gaps which more research studies should be focused on.

The Impact of the Tropical Indian Ocean on South Asian High in Boreal Summer

The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH： warmer SST in the TIO changes the equivalent potential temperature （EPT） in the atmospheric boundary layer （ABL）, alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.