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Abrupt warming of the Red Sea

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Geophysical Research Letters
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D. E. Raitsos
D. E. Raitsos
D. E. Raitsos
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Ibrahim Hoteit at King Abdullah University of Science and Technology
Ibrahim Hoteit
Perdana Prihartato at Saudi Aramco
Perdana Prihartato
Themis Chronis at University of Alabama in Huntsville
Themis Chronis
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Abstract and Figures

Coral reef ecosystems, often referred to as "marine rainforests," concentrate the most diverse life in the oceans. Red Sea reef dwellers are adapted in a very warm environment, fact that makes them vulnerable to further and rapid warming. The detection and understanding of abrupt temperature changes is an important task, as ecosystems have more chances to adapt in a slowly rather than in a rapid changing environment. Using satellite derived sea surface and ground based air temperatures, it is shown that the Red Sea is going through an intense warming initiated in the mid-90s, with evidence for an abrupt increase after 1994 (0.7C difference pre and post the shift). The air temperature is found to be a key parameter that influences the Red Sea marine temperature. The comparisons with Northern Hemisphere temperatures revealed that the observed warming is part of global climate change trends. The hitherto results also raise additional questions regarding other broader climatic impacts over the are.
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Abrupt warming of the Red Sea
D. E. Raitsos,
1
I. Hoteit,
1
P. K. Prihartato,
1
T. Chronis,
2
G. Triantafyllou,
2
and Y. Abualnaja
1
Received 30 April 2011; revised 5 June 2011; accepted 8 June 2011; published 19 July 2011.
[1] Coral reef ecosystems, often referred to as “marine
rainforests,” concentrate the most diverse life in the
oceans. Red Sea reef dwellers are adapted in a very warm
environment, fact that makes them vulnerable to f urther
and rapid warmin g. The detection and understa nding of
abrupt temperature changes is an important task, as
ecosystems have more chances to adapt in a slowly rather
than i n a rapid changing environment. Using satellite
derived sea surface and ground based air tem peratures, it is
shown that the Red Sea is going through an intense
warming initiated in the m id‐90s, with evidence for an
abrupt increase after 1994 (0.7°C difference pre and post the
shift). The air temperature is fo und to be a key para meter
that influences the Red Sea marine temperature. The
comparisons with Northern Hemisphere temperatures
revealed that the observed warming is part of global climate
change trends. The hitherto results also raise additional
questions regarding other broader climatic impacts over
the area.
Citation: Raitsos, D. E., I. Hoteit, P. K. Prihartato,
T. Chronis, G. Triantafyllou, and Y. Abualnaja (2011), Abrupt
warmingoftheRedSea,Geophys. Res. Lett., 38, L14601,
doi:10.1029/2011GL047984.
1. Introduction
[2] The Red Sea holds one of the most diverse marine
ecosystems in the world, although fragile and vulnerable to
oceanic warming [Cantin et al., 2010]. While global
warming is evident across most of the tropical and sub-
tropical seas, the Red Sea warming in particular appears to
exceed the average marine tropical tempera tures [Kleypas
et al., 2008]. It is well documented that the consequences
of the intense warming are apparent across the entire
marine food web, i.e., from primary producers to top‐
predators, which can potentially lead to ecological break-
downs [Beaugran d, 20 04; Richardson and Schoeman,
2004]. For instance, the increased warming has signifi-
cantly slowed down the coral growth in the central Red Sea
[Cantin et al., 2010], while in other cases it has resulted in
the calcification cessation, coral bleaching (zooxanthellae
loss) and mortality. In the past, the Earth’s ecosystem has
repeatedly gone through large climate changes [Alley et al.,
2003]. However, it is the speed of change that controls the
level of response of the ecological communities. In other
words, the ecological systems would have more chances to
adapt in a slowly, rather than in a fast changing environment
[Alley et al., 2003; deYoung et al., 2008]. Thus, particularly
during the last decade there is a growing scientific interest in
the detection and understanding of sudden changes or eco-
system regime shifts.
[
3] The Advanced Very High Resolution Radiometer
(AVHRR) Pathfinder data set has been characterized as the
most extended time series of global sea surface temperature
(SST) currently available [Nykjaer, 2009]. Although it was
not initially intended to be used as a proxy in climate
studies, it has been proved highly valuable for studying
trends and anomalies over long time periods [Marullo et al.,
2007; Nykjaer, 2009]. Despite the importance, there is no
up‐to‐date detailed study assessing the Red Sea thermal
regime through AVHRR. The goal of this study is to report
the satellite derived spatiotemporal changes of the Red Sea
temperatures, and assess whether the alterations observed
during the last two decades originate from regional phe-
nomena, or they are in part driven by global climate change
trends.
2. Methods
2.1. Data Sets
[
4] For this study, three different sources of temperature
data were used, encompassing a period between 1985 and
2007. Here we used the monthly SST means (4 × 4 km
2
)of
the AVHRR Pathfinder V5 data set, which is produced
jointly by the National Oceanic and Atmospheric Admin-
istration (NOAA), and the National Aeronautics and Space
Administration (NASA). To avoid the solar radiation bias
that occurs during the day‐time from surface heating, only
the nighttime overpasses were employed [Nykjaer, 2009;
Raitsos et al., 2006]. The accuracy of the satellite derived
SSTs are documented in numerous studies [Nykjaer, 2009;
Marullo et al., 2007, and references therein]. A recent
detailed ground‐truth validation study in the Mediterranean
Sea reported that the AVHRR Pathfinder data related to an
average error of less than 0.1 K, while although satellites
retrieve the temperature of the skin of the sea surface, the best
fit was found at 4m depth [Marullo et al., 2007]. The authors
further reported that the error appeared to be weekly depen-
dent on season, while it did not drift with time. Both afore-
mentioned features make the Pathfinder SST a dependable
data set for studying global and regional trends and anomalies
[Marullo et al., 2007].
[
5] Monthly means of the in situ air temperature data
were obtained from the King Abdulaziz International Air-
port (KAIA), provided by the Presidency of Meteorology
and Environment (PME) of Saudi Arabia. The Northern
Hemisphere Temperatures (NHT) were acquired from the
1
Red Sea Research Centre, King Abdullah University for Science and
Technology, Thuwal, Saudi Arabia.
2
Hellenic Centre for Marine Research, Institute of Oceanography,
Anavyssos, Greece.
Copyright 2011 by the American Geophysical Union.
0094‐8276/11/2011GL047984
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L14601, doi:10.1029/2011GL047984, 2011
L14601 1of5
Climatic Research Unit and H adley Centre [Jones et al.,
2008] and employed as anomalies relative to the 1961–
90 reference period [Brohan et al., 2006]. The 1000hPa
level monthly gridded geopotential height (m) from the
National Center for Environmental Prediction‐Department
Of Energy Reanalysis II (NCEP‐DOE) was also used for
the same period [Kalnay et al., 1996; Saha et al., 2006].
2.2. Data Analysis
[
6] A regime shift index (RSI) combined with an automatic
sequential algorithm [Rodionov, 2004] was employed to
confirm the existence and statistical significance of abrupt
changes in the data. The absolute value of RSI represents the
magnitude of the shift(s) while its sign determines the change
in direction of mean between regim es (see Rodionov [2004]
for more information). The data were de‐seasonalised
(standardized anomalies) to reduce temporal autocorrela-
tion. Pearson correlation and cross‐correlation analysis were
used to examine the relationships between the data sets.
Here it has to be mentioned that the correlation coefficient
and its significance level were reduced when performed on
de‐seasonalised data (compared to the original one). How-
ever, the seasonality within the monthly temperature time
series is very strong and thus should be removed prior to the
statistical analysis.
3. Results and Discussion
[7] The monthly SST anomaly time series revealed an
abrupt warming that was initiated in 1994, while it was
stabilized to the new warmer state few years later (Figure 1a).
The warming trend is apparent in every month, implying that
the change is not driven by seasonality. The most pro-
nounced signals in this anomaly plot are the relatively colder
winter of 1992 and the relatively warmer summer of 1995
and 1998. Using the NHT anomalies [Jones et al., 2008] it
has been shown that the years 1995 and 1998 have ranked as
the warmest years of the Northern Hemisphere, while the
temperature shift at the end of the 1990s was the most intense
change in the last 160 years [Raitsos et al., 2010]. While the
satellite derived Red Sea SST data set revealed an intense
and abrupt warming in the mid‐90s, this may be part of a
more widespread temperature shift seen in NHT at the
beginning of the 80s [Brohan et al., 2006; Jones et al., 2008].
In addition, the features revealed from the SST differences
prior (1985–1993) and after (1994–2007) the abrupt change,
clearly underlines that the oceanic warming is evident over
Figure 1. Temporal and spatial patterns of long ‐ term satellite derived sea surface temperatures of the Red Sea for the
period of 1985 to 2007. (a) Monthly time series of SST standardized anomalies (the blue colors represent a relatively colder
period, while the red colors a warmer one), and (b) temperature differences (°C) between the two decades, prior and post the
abrupt SST shift (1985–1993 and 1994–2007 respectively). (Note that the scale represents only positive anomalies as neg-
ative ones were not apparent.)
RAITSOS ET AL.: RED SEA CLIMATE DRIVEN WARMING L14601L14601
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the entire Red Sea (Figure 1b). The average difference
between the two decades registers around +0.62°C and in
some areas exceeds the 1°C. It is the central part of the study
area that portrays the highest deviations from the mean. This
is in accordance with Cantin et al. [2010] reporting that the
level of warming of the central Red Sea exceeds the observed
mean tropical warming, an area that holds a very high
diversity of corals.
[
8] In order to examine whether the observed warming
trends is a regional (Red Sea) characteristic or part of the
current global warming trends, we used the NHT data set
(Figure 2a). The results are presented as the 6 month moving
averages to reduce the excess noise of monthly means. The
NHT and the regional SST anomaly data sets parallel one
another at a significant level, showing that the Red Sea
temperature is influenced by the Northern Hemisphere
trends (on a monthly r = 0.44, p = 0.0001, and annual
scale r = 0.73, p = 0.0001). To further assess the mecha-
nism behind the marine warming in the study area, monthly
anomalies of the in situ air temperatures were plotted against
the regional SST ones (Figure 2b). The marine temperature
anomalies strongly parallel the in situ air temperature one
(r = 0.62, p = 0.001), indicating the climatic influence on
the Red Sea warming. Strong correlation is also docu-
mented at an annual base (r = 0.78, p = 0.0001). (Note that
the correlation between the original monthly SST and air
temperature, prior to seasonality removal, was r = 0.96, p <
0.00001.) Cross‐correlation analysis indicated that the best fit
between SST and air temperatures occur at 1 month lag (for
SST). In other words, the air temperature is found to be a key
parameter that influences the Red Sea marine temperature, as
it changes first and approximately 1 month later, the alteration
is observed in the sea. The effect and the timing of the
atmospheric forcing (air temperature) on the Red Sea shown
herein, is consistent with findings from surrounding regions
such as the Mediterranean Sea [Astraldi et al., 1995; Raitsos
et al., 2010]. Finally, the NHT appeared to be significantly
Figure 2. Moving averages (6 month) of the monthly de‐seasonalised regional (marine and air) and Northern Hemisphere
temperatures (1985–2007). (a) Monthly standardized anomalies of the Red Sea SST against NHT, (b) monthly standardized
anomalies of the Red Sea SST versus in situ air temperature. The solid gray line stands for the SST, while the black one for
the NHT and air temperature anomalies respectively.
Figure 3. Red Sea annual time series of SST and minimum
air tem perature values since 1985, along with their seasonal
cycles. (a) Annual SST (°C) against minimum air temperature
values (°C). The gray solid line represents the statistical sig-
nificant regime shifts using Rodionov’s automatic sequential
algorithm. (b and c) Seasonal cycles of SST and minimum air
temperature, along with the averaged difference ( °C) before
and after the shift (1985–1993 and 1994–2007 respectively).
RAITSOS ET AL.: RED SEA CLIMATE DRIVEN WARMING L14601L14601
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correlated with the in situ annual and monthly air temperature
anomalies (r = 0.56, p = 0.003 and r = 0.3, p = 0.001,
respectively) indicating that the anomaly signals and trends
evident in regional air temperatures, which in sequence
influence the Red Sea SST are related to the climate
anomalies of the Northern Hemisphere.
[
9] The analysis of the long‐term (1985–2007) annual
AVHRR SST revealed that not only the Red Sea is warming
rapidly, but there is evidence of a temperature abrupt shift
around 1994 (Figure 3a). It can be observed that before 1994
the annual SST mean remains below the overall mean,
whereas after the abrupt shift the opposite pattern is
observed. During the first decade (1985–1993) the annual
SST mean was 27.4°C, whereas during 1994–2007 the
mean was 28.1°C (0.7°C difference). This result is con-
firmed (using Hadley SST data), as it is reported that the
Red Sea has changed by 0.74°C between 1982 and 2006
[Belkin, 2009]. The coldest registered year was 1992 after
which a stepwise increase is evident (Figure 3a). Further-
more, the abrupt SST shift is related to a statistically sig-
nificant change as the latter is assessed by the Rodionov’s
regime shift detection algorithm (year = 1994, RSI = 1.02,
p < 0.0001). It is noteworthy that after the aforementioned
stepwise increase, the SST has remained warmer without
returning to its initial state. Additional analysis on in situ air
temperature data revealed that the most extensive change
was evid ent in terms of the minimu m values. Fig ure 3b
shows that the lower minimum air temperatures have
increased rapidly after 1994 (RSI = 0.46, p = 0.002). Sea-
sonal cycle analysis of both temperatures showed that the
most prominent alterations occurred during the summer
months (July and August), along with smaller changes dur-
ing the winter months with a peak in February (Figures 3b
and 3c). Similar results are obtained if analysis is per-
formed in maximum as well as in total values, however the
changes are more pronounced in the minimum air tempera-
ture values. August and February are also the months that
have changed the most in the eastern Mediterranean Sea
[Raitsos et al., 2010]. The winter months and particularly
February are very critical for primary production (for both
the Red and Mediterranean Seas) as they are related to the
phytoplankton blooms that are primarily formed due to the
intense water column mixing. Increasing SSTs lead to more
stratified conditions associated with reduced vertical mixing
and thus nutrient availability in the upper oceanic layer. Such
a situation can be detrimental to phytoplankton, which forms
the base of the marine food chain [e.g., Raitsos et al., 2011;
Richardson and Schoeman, 2004].
[
10] The majority of the hitherto findings concern SST
spatiotemporal trends, and how these are related to the
broader changes seen in the Northern Hemisphere. To extend
our working hypothesis, we investigate the involved proxy
variable (i.e., SST) as a potential climate forcing regulator for
the Red Sea area. Although not a direct recipient, the Red Sea
bears few characteristics of the summer monsoonal regime
(southwestern phase) dominant over the Arabian Sea and the
Indian Ocean [Patzert, 1974]. These pertain to the north-
eastward expansion of the Arabian peninsula thermal low,
which further interacts with the low level circulation known
as the Somali Jet [Krishnamurti et al., 1 976]. Figure 4a
illustrates the summer (June to ‐September– monsoonal
season) 1000hPa level geopotential height composite for
the period 1985–2007, where the dominant low pressure
system over the Arabian peninsula extends over the Red
Sea. At the same time and despite the fact that precipitation
over the area is very low (2–3 inches per year [Wang , 2006])
other feedback mechanisms may strongly implicate SST as a
climate regulating factor. The herein documented SST
warming trends are expected to favor additional evaporation,
hence the deepening of the regional low pressures over the
area is likely. In turn, Figure 4b illustrates the respective
numerical geopotential height difference prior to and after the
herein documented SST abrupt change (1985–1993 period
minus 1994–2007). It becomes evident that the period 1985–
1993 is followed by an overall lowering of the pressure gra-
dients during 1994–2007 (i.e., positive geopotential height
differences, 1000hPa, in meters) over the Red Sea, fact that
supports the previous hypothesis. Additional implications
arise from the aforementioned pressure re‐distribution and
these pertain to the zonal wind and cloudiness modulation
over the study area. In fact, additional data analysis (not
shown) depicts the intensification of the Somali Jet along
with increased Outgoing Longwave Radiation values for the
period 1994–2007.
4. Conclusion
[11] Regardless of its origin, natural and/or anthropogenic
[Alley et al., 2003], it is widely accepted that oceanic
warming is evident worldwide. The satellite retrieved SST
revealed that the Red Sea is going through an intense
warming that was initiated in the mid‐90s, with evidence of
an abrupt increase after 1994 (a result also shown from the
air temperature data sets). Only during the last decade, the
SST has increased by 0.7°C. Spatiotemporal analysis
showed that the thermal change is apparent in the whole Red
Sea and in the entire year. Comparison with temperatures of
the Northern Hemisphere suggested that the Red Sea
warming is not a local phenomenon but a part of a wide-
spread warming trend that is observed worldwide. In this
view, the marine temperatures appeared to follow the air
temperatures with 1 month delay, indicating the approxi-
mate time needed to see the changes in the sea. It is evident
that the broader climate including atmospheric forcing and
intensity of monsoons have been altered during the period of
Figure 4. Numerical barometric pressure gridded at the
1000hPa level. (a) Composite of June–September surface
geopote ntial height (m) f rom 1985 to 2007, and (b) differ-
ence prior an d after th e SST abr upt change (1985–1993
minus 1994–2007) of June–September surface geopotential
height.
RAITSOS ET AL.: RED SEA CLIMATE DRIVEN WARMING L14601L14601
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SST abrupt shift. This work brings a step closer toward
reporting and understanding a temperature abrupt change
seen in the Red Sea. However, the question as which factor
has triggered this sudden alteration remains unanswered.
Alley et al. [2003] mentioned that even a small and slow
forcing can trigger an abrupt change. The description of the
potential ocean temperature‐lower atmosphere feedback
would need further and detailed investigation.
[
12] An abrupt climate change can potentially occur when
the climate system is forced to overpass a particular
threshold, while their economic and ecological impact could
be significant [Alley et al., 2003]. It is predicted that the Red
Sea temperature will increase as climate change continues
[Cantin et al., 2010], a prediction that will further alter the
regional ecosystem. The level of the Red Sea temperature
change is one of the highest seeing, a result that is confirmed
by other studies. Oceanic warming may have a direct or
indirect impact on marine entities and ecosystems, thus,
there is a need to assess further available past biological data
(e.g., coral, fisheries, plankton) for potential responses to the
new thermal state, and to closely monitor the relatively
unexplored and fragile Red Sea ecosystem.
[
13] Acknowledgments. We thank the Presidency of Meteorology
and Environment (PME) of Saudi Arabia, for providing the air tempera-
ture data. We also thank Igor M. Belkin and one anonymous reviewer for
their constructive comments. This research was supported by the King
Abdullah University for Science and Technol ogy (KAUST), Kingdom
of Saudi Arabia.
[14] The Editor thanks two anonymous reviewers for their assistance in
evaluating this paper.
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... Journal of Marine Systems xxx (xxxx) 104066 ing the East China Sea (e.g., Ji et al., 2018), the Pacific Ocean (e.g., Xu et al., 2021 ), the Indian Ocean (e.g., Seenipandi et al., 2021), and the Black Sea (e.g., Sakalli & Başusta, 2018), amongst others. Over the last decade and more, various attempts have been made to assess spatiotemporal changes in SST across the Red Sea (e.g., Raitsos et al., 2011;Chaidez et al., 2017;Krokos et al., 2019;Agulles et al., 2021;Hereher et al., 2021). This interest was motivated in part by the fact that SST plays a major role in marine habitat changes, and the Red Sea hosts one of the world's most diverse marine ecosystems (Cantin et al., 2010). ...
... While there are a considerable number of studies that have been conducted to analyze changes in SST over the Red Sea, it is important to acknowledge that these investigations have tended to focus on evaluating the variability of SST for the entire Red Sea region, with relatively limited attention given to examining specific local and regional changes (e.g., Raitsos et al., 2011;Chaidez et al., 2017;Krokos et al., 2019;Shaltout, 2019;Agulles et al., 2021;Hereher et al., 2021). These spatial constraints are primarily attributed to the coarse spatial resolution of the gridded SST datasets employed in the majority of studies e.g. ...
... Alawad et al. (2020) observed a warming trend of 0.4°C per decade in the northern Red Sea from 1982 to 2017, compared to only 0.1°C per decade in the southern Red Sea. That finding was also reinforced by Raitsos et al. (2011) who reported that the most notable warming in the Red Sea occurred in the northern and central regions rather than the southern regions. Furthermore, our results demonstrate that the western coasts experienced warmer SST trends compared to the eastern coasts. ...
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  • May 2025
  • J MARINE SYST
A comprehensive analysis of changes in sea surface temperature (SST) was performed across the Red Sea for the period 2003 to 2020 using satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua. Employing a regionalization scheme based on principal component analysis (PCA), five homogenous sub-regions were identified that explain about 85 % of the total variation in SST across the Red Sea. The results indicate that there is a diverse and complex range of SST variability throughout the Red Sea. Spatially, distinct SST trends were observed between the southern (PC1) and northern (PC3) regions, which show northward enhancement in the rate of SST trends. A zonal contrast in the rate of warming over the western and eastern sectors was also observed, exhibiting more pronounced warming trends along the western coasts. In contrast to the offshore and deep waters, surface warming in shallow waters (depth < 100 m) was more pronounced, which poses detrimental effects (e.g., thermal coral bleaching) on regional marine ecosystems. We found a robust link between spatial patterns of SST anomalies and the phases of the Red Sea Dipole (RSD). This connection was largely regulated by the upwelling associated with the local wind-stress-curl. Further, the spatial and temporal patterns of wind-driven upwelling (i.e., coastal and wind-stress-curl-driven upwelling) were reminiscent of the SST trend, highlighting the significant role of the upwelling mechanism in the SST budget and trend across the Red Sea. The positive phase of the RSD aligns with periods of stronger Toker Jet activity, reinforcing cold SST anomalies in the southern Red Sea due to enhanced upwelling-induced cooling. However, the impacts of wind-driven upwelling on local SST differ from region to region, highlighting the need to employ a high-resolution wind dataset in the simulation of SST across the Red Sea. Overall, our findings offer insights into the complex mechanisms and factors influencing SST variability in the Red Sea, thereby contributing to improving coastal zone management and environmental planning efforts.
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... The Red Sea is a rapidly warming Large Marine Ecosystem 24 that has been subject to rising temperatures surpassing global warming rates [25][26][27] . The Red Sea's ecological and economic significance is rooted in its rich marine biodiversity and extensive coral reef ecosystems 28-30 . ...
... Our findings revealed a significant rise in MHW occurrence across the Red Sea, which aligns with the rapidly warming trend of the basin [25][26][27] and the global increase in MHW frequency, intensity, and duration 77,78 . It is worth noting that the increase in MHW days was observed during the winter blooming period and was more pronounced (> 15 days/decade, years 1982-2018) in the central NRS, the western part of the NCRS and the mid-south part of the SCRS, where eddy activity is consistently present 70,79,80 . ...
... This decreasing MCS trend, generally amounting to 10-30 MCS days less per decade, was particularly evident (at least 25 fewer MCS days per decade) in the western NCRS, the eastern SCRS, and in parts of the SRS. The reduction in MCS days may be influenced by the general warming of the basin [25][26][27] . This warming has been attributed to reduced winter atmospheric cooling 86 , while particularly in the southern part of the basin, may be influenced by the intrusion of warm surface waters from the West Indian Ocean (WIO) during winter, through the Bab-el-Mandeb strait 87,88 . ...
Response of Red Sea phytoplankton biomass to marine heatwaves and cold-spells
Article
Full-text available
  • Feb 2025
In tropical oceans, phytoplankton experience significant alterations during marine heatwaves (MHWs), yet the consequences of reduced or absent marine cold-spells (MCSs) on these microscopic algae are currently overlooked. Synergistically combining in situ measurements, Argo-float data, remotely-sensed observations, and hydrodynamic model outputs, we explore such relationships in the Red Sea. Results show a long-term (1982 to 2018) gradual increase in MHW days (5–20 days/decade) and a clear decrease in MCS days (10–30 days/decade). Compound extreme temperature and chlorophyll-a events (Chl-a – an index of phytoplankton biomass) exhibit consistently lower Chl-a concentrations during MHWs and higher ones during MCSs, particularly in the northern and southern Red Sea. In these regions, during the main phytoplankton-growth period, the presence of MHWs/MCSs leads to respective Chl-a anomalies in 94% of the cases. Yet, phytoplankton responses in the central Red Sea are more complex, most likely linked to the region’s highly dynamic circulation (e.g., mesoscale anti-cyclonic eddies), and multiple nutrient sources. In the naturally warm and stratified ecosystem of the Red Sea, where deeper mixed layers enhance the transfer of nutrient-rich waters to the lit zone, the substantial reduction of MCSs could be more impactful for phytoplankton than the gradual rise of MHWs.
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... The Red Sea is categorized as a fast-warming large marine ecosystem (LME) and is surrounded by extensive shallow-water coral reefs possessing rich biodiversity and economic value (Berumen et al., Hoteit et al., 2021). Red Sea coral reefs face increasing risks of bleaching due to local stressors and regional warming (Ellis et al., 2019;Genevier et al., 2019;Gonzalez et al., 2024;Raitsos et al., 2011). Several bleaching episodes have been reported in the Red Sea basin over the past few decades (DeCarlo, 2020;Dosoky, 2021;Furby et al., 2013;Gonzalez et al., 2024;Monroe et al., 2018;Osman et al., 2018). ...
... Many studies also suggested that the magnitude of the optical signal provided by the corals increases when it bleaches and decreases after it bleaches (Andrefouet et al., 2002). Increased SSTs caused by regional warming (Chaidez et al., 2017;Raitsos et al., 2011) negatively impact coral reefs, resulting in more frequent, widespread, and severe bleaching events in the Red Sea. Previous research has demonstrated that the NRS coral reefs are stressed due to maximum SST warming (≤0.8°C per decade) (Hereher et al., 2021). ...
Remotely sensing coral bleaching in the Red Sea
Article
Full-text available
  • Feb 2025
Coral bleaching, often triggered by oceanic warming, has a devastating impact on coral reef systems, resulting in substantial alterations to biodiversity and ecosystem services. For conservation management, an effective technique is needed to not only detect and monitor coral bleaching events but also to predict their severity levels. By combining high‐resolution satellite measurements (Sentinel‐2 Multispectral Instrument) and a bottom reflectance model within a least‐squares approach, we developed a new ocean color remote‐sensing model specifically designed to detect, map, and predict severity levels (low to high) of coral bleaching events at a high spatial resolution of 10 m. The proposed algorithm was implemented and tested within the Red Sea and compared remarkably well with concurrent and independent in situ data. We also applied the algorithm to investigate the response of corals during and after a bleaching event in the Wadi El‐Gemal region (Egypt) from July to December 2020. Our results show that coral bleaching severity levels and sea surface temperature (SST) were unusually high during August–September 2020. After the event, the coral bleaching signal decreased concurrently with SST during October–November 2020, aligned with a recovery of bleached coral reefs by December 2020. The proposed algorithm offers a cost‐effective approach toward developing a near‐real‐time remote‐sensing system for monitoring coral bleaching events and recovery at multi‐reef scales. Such remote‐sensing tools would aid policymakers and managers in developing and implementing integrated management strategies for coral reef conservation, as well as in supporting reactive management plans, including the identification of priority areas for intervention.
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... Effects like these can be especially pronounced in semi-enclosed basins and coastal regions such as the Red Sea basin, where climate-change related phenomena tend to occur at a faster rate than average (e.g., Raitsos et al., 2011;Williams, 2013). ...
Coupled sea-level and hydroclimatic controls on the southern Red Sea sedimentation during the past 30 ka
Article
Full-text available
  • Apr 2025
  • QUATERNARY SCI REV
Sedimentation in the Red Sea basin is governed by the complex interplay between regional atmospheric circulation , precipitation patterns, and sea level fluctuations, which altogether exert a profound control on the detrital and biogenic components of the sedimentary record. To gain a comprehensive understanding of these controls on the southern Red Sea sedimentation over the past 30 ka, we here combine high-resolution bulk geochemical and mineralogical data with detrital grain-size distributions and plant-wax biomarkers at a sub-centennial average temporal resolution. Our proxies reveal that the sedimentary record is characterised by two distinct depositional regimes of detrital and marine origin. The pronounced shift from the detrital-dominated (ca. 30-14.6 kyr) to the marine-dominated phase (ca. 14.6-0.8 kyr) coincides with the end of Heinrich Event 1 and the rapid sea-level rise associated with Meltwater Pulse 1a. Flooding of the shelf during deglacial sea-level rise increased the distance between the core site and the respective shoreline, and partially controlled the delivery of detrital material to the site. Shifts in detrital grain-size distribution and mineralogical composition indicate a reduction in regional continental aridity and potentially weaker wind circulation with the onset of Greenland Interstadial-1, while the reestablishment of water-mass exchange with the Gulf of Aden from ca. 15 ka onwards led to a marine productivity surge at our study area. An increase of fine-grained fluvial material and terrestrial n-alkanes between ca. 16 and 8 ka points to the establishment of more pluvial conditions and the activation of local wadi runoff during the African Humid Period. Finally, the subtle but steady increase of detrital input from ca. 5 ka onwards suggests the re-establishment of continental aridity during the late Holocene.
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... Even slight increases in temperature can critically impair organismal health and result in mass mortality (Genin et al., 2020), despite inherent adaptations to warmer temperatures (Fine et al., 2013). The Red Sea epitomizes this scenario, with a high proportion of endemic marine life (DiBattista et al., 2016) and entire reef systems existing along a thermal gradient with higher background temperatures relative to most other coral reef systems (Chaidez et al., 2017;Raitsos et al., 2011). Insights from warmer than average, marginal reef environments, like the Red Sea, can shed light on how variation in thermal limits influence the functional responses of marine species and provide insight to how those tolerances translate to vulnerability to MHWs . ...
Extreme marine heatwave linked to mass fish kill in the Red Sea
Article
Full-text available
  • Apr 2025
Anthropogenic climate change has precipitated an increase in marine heatwaves (MHWs) that have significant and multifaceted impacts on marine ecosystems. In late August 2023, an intense heatwave coincided with a mass fish kill event on the Saudi Arabian coast of the central Red Sea. Here, we compile MHW metrics from satellite data to illustrate the mortality event was linked with the most intense period of rapid heating in the central Red Sea in recent history. Using field surveys, we quantified the impact of the event on the fish community and found that nearly 1000 fish washed ashore along a 60 km stretch of coastline. Representatives of 54 species were detected, which illustrates the impact of the MHW event on a broad range of fishes. The exact cause of mortality during the event is unknown, but likely related to temperature-induced physiological stress and associated factors. Sparse coastal monitoring limited our ability to rapidly respond to the event and document the proximate cause of mortality. This study not only sheds light on the immediate impacts of a MHW on components of a coral reef ecosystem, but also emphasizes the broader ecological consequences. Mass fish kills may have cascading impacts on ecosystem functioning by causing shifts in community structure and a decrease in biodiversity, which can undermine both the ecological functioning and economic stability of marine-dependent regions. This may be especially true for reefs already occupying a thermal niche that approaches the upper limits of many species, such as those in the Red Sea. Our study highlights the critical need for enhanced reporting mechanisms and forecasting tools to effectively document and help mitigate further impacts linked to MHW-induced mass marine die-offs.
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... The fossil records, combined with insights into the current state of coral reefs, underscore the importance of understanding environmental preferences, geographic distributions and adaptive strategies to inform conservation efforts. Elevated summer temperatures in the central and southern Red Sea compound the vulnerability of coral species like D. heliopora, where calcification rates have declined significantly over recent decades due to warming events, as noted by (Cantin et al. 2010;Raitsos et al. 2011). Moreover, this study highlights the critical need to detect population declines before thresholds of extinction are reached, emphasising the role of fossil records in identifying at-risk species. ...
First Record of Three Pleistocene Scleractinian Coral Families in Seir Peninsula, Farasan Islands: Expanding Red Sea Biodiversity
Article
The Pleistocene reef terraces of the Red Sea serve as a valuable geological archive, reflecting past marine conditions and environmental fluctuations. Among these, the Farasan Islands, located in the southern Red Sea off the Saudi Arabian coast, host a remarkable diversity of coral families, including Acroporidae, Agariciidae, Euphylliidae, Fungiidae, Lobophylliidae, Merulinidae, Pocilloporidae, and Poritidae, underscoring the region's ecological significance during the Pleistocene epoch. This study focuses on the taxonomy, biogeography, and evolutionary trends of three previously unreported scleractinian coral families Diploastraeidae, Pachyseridae, and Rhizangiidae from the Pleistocene reef units at the Seir Peninsula, Farasan Islands. We document, for the first time, the occurrence of Diploastrea heliopora and Pachyseris inattesa in the Pleistocene of the Red Sea, with P. inattesa representing the first known fossil record of this species globally. A comparison between Pleistocene and extant populations reveals a significant decline in D. heliopora abundance, reflecting substantial environmental and ecological shifts over time. P. inattesa , historically misidentified under different taxonomic names, is an endemic Red Sea species with a cryptic nature, whose first fossil occurrence in this study provides new insights into its evolutionary history and biogeographic distribution. This study advances our understanding of coral diversity and environmental changes in the Red Sea's Pleistocene reefs. It highlights the importance of fossil records in tracking biodiversity shifts and underscores the need for further research on the geographic distribution and conservation of these coral genera.
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... The warm and oligotrophic nature of the Red Sea makes it particularly susceptible to the effects of warmer conditions. Recent studies have reported that the Arabian Peninsula experiences higher rates of warming compared to other regions [42], resulting in both physical changes [43][44][45], and biological responses in coral reef ecosystems [46][47][48] and in phytoplankton biomass [24,35]. Given this vulnerability, understanding the current control of MLD variability on nutrient distribution in the Red Sea basin is important. ...
Unravelling the influence of mixed layer depth on chlorophyll-a dynamics in the Red Sea
Article
Full-text available
Primary production in highly stratified and oligotrophic tropical seas relies primarily on nutrient injections from a deepened mixed layer. The Red Sea, one of the warmest marine ecosystems on earth, has very few external nutrient sources. The role of mixed layer depth (MLD) on phytoplankton dynamics has predominantly been investigated in the northern part of the basin, yet a comprehensive investigation covering the entire basin is currently lacking. By integrating numerical MLD simulations and ocean colour remote sensing observations, both regionally-tuned to the Red Sea environment, the influence of vertical mixing, proxied by the MLD, on chlorophyll-a concentration (CHL) is investigated at seasonal and interannual scales. Results show that the central basin exhibits weak relationships, possibly linked to the intense mesoscale activity and the resulting horizontal advective fluxes. Remarkably, in the southern basin, even minor MLD variations (3%) seem to have a significant response in CHL (~10%). Until now, phytoplankton biomass in the south was linked to the horizontal intrusion of nutrient-rich waters from the Indian Ocean, while our results also stress the importance of vertical mixing in the redistribution of these fertile deeper layer waters to the surface lit zone. Here, we report the diverse role of deepened mixed layers in shaping CHL concentrations across various provinces in the Red Sea.
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... rumen et al., 2019). It is extremely warm and saline, with the sea surface temperature (SST) reaching up to 35°C in summer and sea surface salinity (SSS) reaching up to 40.5 psu (Carvalho et al., 2019;Yao, Hoteit, Pratt, Bower, Zhai et al., 2014;. It has been reported to be abruptly and rapidly warming over the recent decades (Chaidez et al., 2017;D. E. Raitsos et al., 2011). Marine organisms living in such a warm regional sea may be operating at the high end of their thermal tolerance, making the Red Sea a natural laboratory for marine ecosystem studies under the context of global warming (Chaidez et al., 2017;. Therefore, it is increasingly important to understand the Red Sea ecosystem, such as its CHL (a ...
Observations and Biogeochemical Modeling Reveal Chlorophyll Diel Cycle With Near‐Sunset Maxima in the Red Sea
Article
Full-text available
The Red Sea is an extremely warm tropical sea hosting diverse ecosystems, with marine organisms operating at the high end of their thermal tolerance. Therefore, in the context of global warming, it is increasingly important to understand the Red Sea ecosystem, including the variability of chlorophyll at different spatiotemporal scales. Using a coupled physical–biogeochemical model and in situ data, we investigate and quantify the diel cycle in Red Sea chlorophyll concentration for the first time, revealing near‐sunset chlorophyll maxima at 17 ± 1 hr local time over the entire basin. This chlorophyll peak time is considerably later than those reported in most other oceans, reflecting the previously reported high irradiance and further suggesting potentially low grazing rates in the Red Sea. Model‐based analyses reveal that chlorophyll diel cycle is predominantly controlled by light‐driven circadian rhythm (i.e., irradiance), whereas longer‐timescale (e.g., seasonal) chlorophyll variability is regulated by nutrient availability, suggesting a light‐limited biological production on a diel timescale and a nutrient‐limited production on a seasonal scale. The identified chlorophyll diel cycle comprises a fundamental component of the Red Sea ecology and has implications for chlorophyll remote sensing and in situ measurements. Our findings indicate that future field studies investigating phytoplankton growth and zooplankton grazing dynamics—such as phytoplankton community composition and zooplankton diel vertical migration—are still needed to further elucidate the revealed chlorophyll diel cycle in this potentially unique tropical sea.
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... In particular, the northern Red Sea has experienced mild (<10% coral cover) bleaching events so far 9 , while moderate (<30%) and severe (>50%) bleaching has been observed in the north-central and south-central Red Sea in 1998, 2010 and 2015 [10][11][12][13] . These events coincide with an abrupt warming seen throughout the basin 14 , that has also led to an increase in the frequency, duration and severity of MHWs over the past few decades 15 , particularly in the northern Red Sea, which is the region exhibiting the highest warming rate 8 . ...
Drivers of marine heatwaves in coral bleaching regions of the Red Sea
Article
Full-text available
  • Feb 2025
Extreme warm ocean temperature events, known as marine heatwaves, have been associated with several coral bleaching reports in coastal locations of the Red Sea. Yet, our knowledge of the processes driving these events remains limited. Here we analyse the upper ocean mechanisms behind multiple summer marine heatwaves between 2001 and 2015, over known coral bleaching-affected regions, using a high-resolution ocean model, specifically tuned for the Red Sea. Our findings indicate atmospheric forcing as the primary driver of marine heatwave onsets in the northeast and southwest, while horizontal advection plays a key role in the southeast and northwest coasts. While the frequency and associated temperature changes of the events’ main drivers are subject to regional influences, the intensity and duration of extreme warming due to horizontal advection, on average, exceed that of atmosphere heat fluxes, which act as the major cooling mechanism across the majority of study areas. Ecological threats for Red Sea corals are further highlighted with a view to enhance our understanding of their response to climate change.
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Links between sea surface temperature anomalies and seismic activity in the Red Sea across multiple temporal scales
Article
Full-text available
  • May 2025
This study evaluates the links between seismic activity and sea surface temperature (SST) variability in the Red Sea from 2003 to 2020. We utilized the Egyptian National Seismic Network (ENSN) and ISC-GEM Global Instrumental Earthquake Catalogue (version 9.0) provided by the Global Earthquake Risk Model (GEM) Organizations and the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite SST data. Trend analysis indicates that the northern and southern regions exhibited distinct SST changes, with a robust gradient of warming signals from the north to the south. In addition, we assessed the association between seismic activity and SST anomalies across various timescales (daily, annual, and decadal) in the Red Sea. Overall, results suggest a consistent negative correlation between SST changes and seismic activity at the multidecadal and annual scales. At these longer timescales (i.e., annual and decadal), seismic events, even with micro magnitudes (less than 3) as in the northern Red Sea, may contribute to localized and slow negative SST anomalies. This negative feedback may be attributed to the reduction in hydrostatic pressure on the sea crust as a result of the formation of new crusts in response to the divergence of tectonic plates. On the other hand, at shorter scales (daily or weekly), the results indicate SST warming before seismic events and SST cooling during and after the seismic events. This pattern indicates that lithostatic pressure changes and geothermal flux are likely to impact SST shortly before seismic activity. Nevertheless, the long-term variability of SST is less significantly impacted by these localized and short-term anomalies. Overall, the intricacy of SST-seismic interactions has implications for acquiring and understanding the behavior of the dynamic marine environment and earthquake forecasting, but further studies are needed to confirm these potential interactions.
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Macroscale factors affecting diatom abundance: a synergistic use of Continuous Plankton Recorder and satellite remote sensing data
Article
Full-text available
  • Mar 2011
Diatoms exist in almost every aquatic regime; they are responsible for ∼20% of global carbon fixation and ∼25% of global primary production, and are regarded as a key food for copepods, which are subsequently consumed by larger predators such as fish and marine mammals. A decreasing abundance and a vulnerability to climatic change in the North Atlantic Ocean have been reported in the literature. In the present work, a data matrix composed of concurrent satellite remote sensing and Continuous Plankton Recorder (CPR) in situ measurements was collated for the same spatial and temporal coverage in the Northeast Atlantic. Artificial neural networks (ANNs) were applied to recognize and learn the complex non-monotonic and non-linear relationships between diatom abundance and spatiotemporal environmental factors. Because of their ability to mimic non-linear systems, ANNs proved far more effective in modelling the diatom distribution in the marine ecosystem. The results of this study reveal that diatoms have a regular seasonal cycle, with their abundance most strongly influenced by sea surface temperature (SST) and light intensity. The models indicate that extreme positive SSTs decrease diatom abundances regardless of other climatic conditions. These results provide information on the ecology of diatoms that may advance our understanding of the potential response of diatoms to climatic change.
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A Sequential Algorithm for Testing Climate Regime Shifts
Article
Full-text available
  • May 2004
Empirical studies of climate regime shifts typically use confirmatory statistical techniques with an a priori hypothesis about the timing of the shifts. Although there are methods for an automatic detection of discontinuities in a time series, their performance drastically diminishes at the ends of the series. Since all the methods currently available require a substantial amount of data to be accumulated, the regime shifts are usually detected long after they actually occurred. The proposed sequential algorithm allows for early detection of a regime shift and subsequent monitoring of changes in its magnitude over time. The algorithm can handle the incoming data regardless whether they are presented in the form of anomalies or absolute values. It can be easily used for an automatic calculation of regime shifts in large sets of variables.
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The Asian Monsoon
Book
  • Jan 2006
Satellite observations and computing technology have advanced our understanding of the monsoon climate enormously in the last two decades. The author provides an update of the knowledge gained over this period, presenting the modern morphology and the physical principles of monsoon climate variation on all time scales ranging from intraseasonal to tectonic time scales. He brings new ideas that can be expected to markedly improve the prediction of monsoon climate, and includes contributions by experts who expand our understanding of the monsoon environment by their study of paleoclimate records, who present evidence of human influences on monsoon climate, and who describe the links of the monsoon to the economy and to human health. This is a comprehensive interdisciplinary text book summarizing new knowledge of Asian monsoon climate variability, dynamics, modeling, and prediction from intraseasonal to geological time scales, and human influence and its links to environmetal/economic issues.
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Abrupt Climate Change
Article
  • Nov 2004
The abrupt climatic changes during winters and sudden droughts scorching farmland around the globe are discussed. Global warming is pushing the earth's climate faster towards sudden shifts and has become a matter of great concern. A gradual change in temperature or other physical conditions pushed the key driver of the climate towards a invisible threshold. The studies show that within several thousand years after the start of a typical warm period, the climate reverted to slow cooling followed by quick cooling over as short a time as a century.
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Abrupt Climate Change: Overview
Article
  • Dec 2001
Paleoclimatic records show that large, rapid, widespread climate changes have occurred repeatedly. Thresholds and feedbacks in the Earth system impart abruptness and persistence, so it is likely that abrupt climate changes will occur in the future. A new National Research Council study of abrupt climate changes, sponsored by the U.S. Global Change Research Program, highlights the strong evidence for abruptness in past climate changes, regionally as well as globally and affecting water and other climatic variables in addition to temperature. Our understanding of mechanisms identifies many key areas and climate variables involved in abrupt changes, but does not provide predictive capability beyond the realization that further abrupt changes are likely. Abruptness increases the impacts of climate changes on societies and ecosystems. A tartgeted reesearch program of paleo- and modern studies of climate change and impacts, including analysis of mechanisms and improved statistical characterization, would significantly increase understanding of abrupt changes and allow improved recommendations of mitigation or adaptation strategies.
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Mediterranean Sea surface warming 1985–2006
Article
  • Apr 2009
Satellite observations from 1985-2006 indicate that in the last 2 decades the temperature in the upper layer of the Mediterranean Sea has been increasing at an average (+/- SD) rate of 0.03 +/- 0.008 degrees C yr(-1) for the western basin and 0.05 +/- 0.009 degrees C yr(-1) for the eastern basin. The increases in temperature are not constant throughout the year but occur primarily during May, June and July. Maximum increases of 0.16 degrees C yr(-1) are found in June in the Tyrrhenian, Ligurian and Adriatic Seas and close to the African coast. The Aegean Sea shows maximum change in sea surface temperature during August. Only the statistically significant results are presented.
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