Biological and Chemical Response of the Equatorial Pacific Ocean to the 1997-98 El Niño

“…trends of the marine biota (Venrick et al., 1987; Karl et al., 1995; McGowan et al., 1998), potentially driven by changes in trace metal supply (Jickells et al., 1998; Chavez et al., 1999), changes in nitrogen fixation (Karl et al., 1995), or changes in mixed-layer depth (Freeland et al., 1997).”

“…cycles by humans (Valiela et al. 1997, Vitousek et al. 1997), large-scale environmental perturbations such as El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO; Barber and Chavez 1983, Chavez et al. 1999), and human-induced climate change (Post and Pedersen 2008).”

“In all four regions, interannual variability is evident in the two years examined, most notably in the two Pacific EBCs (California and Humboldt), where the strong 1997–1998 El Nino event caused large hydrographic and biological anomalies ( Chavez et al. 1999 , Thomas et al.”

“Some of the best data on climate impact available at this time refer to EN as a consequence of the fact that the two strong EN events 1982–1983 and 1997–1998 were exceptionally well documented (e.g. Barber and Chávez 1983; Chávez et al. 1999; Tarazona et al. 2001).”

“The effects off Central (Chavez et al., 2002) and Southern California (Bograd & Lynn, 2001) were similar to those in the equatorial Pacific (Chavez et al., 1999).”

“End products derived from SeaWiFS imagery are extensively used for the study of marine phytoplankton biomass distribution and production (e.g., [ 2 ]‐[5]), and of aerosol load (e.g., [6] and [7]).”

“While several moored sensor systems have been deployed in the more classical oceanic case 1 remote sensing environments (Clark et al., 1997; Chavez et al., 1999; Dickey et al., 1998, 2001), few have been deployed in more optically complex case 2 environments.”

“…to December, when the Humboldt Current increases in intensity and the EF moves north and settles just north of the GA (Palacios 2004) In addition, periodical climatic disturbances, such El Niño Southern Oscillations (ENSO), significantly affect the marine communities of the GA (Chavez et al. 1999)”

“[12] The mean chlorophyll value for the central region (Figure 4b), based on both satellite and in situ measurements, is very close to the 0.21 mg m 3 calculated for 1980–1998 [Chavez et al., 1999].”

“…Dalian is from 1980 to 1997, which are from different eras and may defy comparison because the 1997–1998 El Niño is one of the strongest in the 20th century (Chavez et al., 1999) and changes many of the physical oceanic properties (Nezlin and Mcwilliams, 2003; Shang et al., 2005; Liu et al., 2010).”

“For example, a phytoplankton bloom of exceptionally large spatial extent developed in the equatorial Pacifi c after the 1997–98 El Nin ˜o event ( Chavez et al., 1999 ).”

“For example, in the tropical Pacific, some Tropical Atmosphere Ocean (TAO) moorings are now equipped with infrared CO2 instruments [ Chavez et al., 1999 ] and in the Baltic Sea a SAMI-CO2 sensor [DeGrandpre et al., 1995] was installed on a moored platform [Kuss et al., 2006] but high frequency measurements are still s…”

“Such an index has previously been found to have major impacts on phytoplankton and fisheries (Barber and Chavez, 1983; Chavez et al., 1999; Behrenfeld et al., 2001).”

“In contrast to the moderate 1991-1992 El Niño when nitrate persisted at the surface [McCarthy et al., 1996], no nitrate is measured in the surface layer in the central Pacific [Chavez et al., 1999] in 1997.”

“Such a response was also indicated by in situ (Chavez et al., 1999), dynamic (Gorgues et al., 2010) and some remote sensing (Masotti et al., 2011) modeling studies, which report that diatoms first decreased and later increased significantly in response to El Niño and La Niña, respectively.”

“[2] El Niño is known to result in interannual climate fluctuations over the Pacific Ocean, which in turn cause variability in biological production and ecosystem dynamics [e.g., Murtugudde et al., 1999; Chavez et al., 1999; McClain et al., 2002; Wang et al., 2005].”

“…consequences of marine phytoplankton change derive from studies of the effects of quasiperiodic climate fluctuations, for example from the El Nino Southern Oscillation or North Atlantic Oscillation (NAO; Barber & Chavez 1986, Chavez et al. 1999, Behrenfeld et al. 2006, Martinez et al. 2009).”

“Interannual variability of CO2 growth is correlated with ENSO (El Nino Southern Oscillation) variations of tropical temperatures (figure 2).”

“Generally, upwelled water bears the signature of organic matter remineralization, including high pCO2 and nutrient content [ Chavez et al., 1999; Feely et al., 2006] and low O2 content [Hendricks et al., 2005; Kaiser et al., 2005].”

“The thermal and nutrient shift in the Pacific during this transition resulted in the recovery of the phytoplankton community following an extended period of impoverishment during the El Niño years preceding it (Chavez et al. 1999).”

“In fact, an observational study showed that a phytoplankton bloom in the upper ocean can induce a significant drawdown of atmospheric carbon dioxide (CO2), implying the existence of ocean biology-induced climate feedback from a geochemical viewpoint (Chavez et al. 1999).”

“Other organisms have also been reported to experience changes in their population abundance including algae, invertebrates, larval fish, seabirds, and marine mammals (Soto 1985; Tomicic 1985; Castilla and Camus 1992; Massey et al. 1992; Arntz and Fahrbach 1996; Tsai et al. 1997; Arcos et al. 2001; Riascos 2002; Fiedle…”

“Diatoms and picoplankton are dominant during La Niña and El Niño phases, respectively (Chavez et al., 1999).”

“[10] The presence of warm surface waters along the Peruvian coast increases stability in the water column, enhances stratification, and thus, reduces nutrient supply, primary productivity, and ultimately TOC flux to the sediment [Chavez et al., 1999].”

“The El Nin˜o event of 1997–1998 was one of the strongest on record and it reached its peak in the winter of 1998 [ Chavez et al. , 1999] (Winter in a given year is defined in this paper as the three-month period between December 1 of the preceding year through the February of the given year).”

“In the eastern equatorial Pacific, changes in net primary productivity are especially sensitive to the effects of Kelvin waves on the depth of the nutricline [Chavez et al., 1999].”

“The positive effect of stormwater nutrient discharge may have been counterbalanced by negative effect of stronger than normal nutrient limitation that resulted from El Niño-driven deep pycnocline (e.g., Chavez et al. 1998, 1999).”

“1998, an unprecedented phytoplankton bloom appeared at the equator as described by Chavez et al. [1999] .”

“The central Pacific provides an opportunity to explore the impact of declining pelagic subsidies, primarily nutrient concentrations and planktonic biomass, to coral reefs during heat waves because sea surface temperature and primary production are inversely related during strong El Niños ( 14 ).”

“2013), owed to its dramatic societal and economical consequences (Glantz 2001; Chavez et al. 1999), it is now recognized that a substantial share of the interannual SST variability in the tropical Pacific is associated with moderate El Niño events (Rasmusson and Carpenter 1982; Ashok et al.”

“The phenomenon influences not only climate and biosphere, but also the economies of several countries through impacts on agriculture and fisheries, thereby affecting human societies in many different ways [McPhaden et al., 2006; Chavez et al., 1999].”

“, 1993; Ciais et al., 1995, Francey et al., 1995). Randerson et al. (2002) invoked irregular discrimination as a way to reconcile differences in variability between isotopic and non-isotopic calculations of land and ocean fluxes.”

“Expected marine features can be observed from these monthly averaged patterns: The chlorophyll bloom distorted by tropical instability waves in the Equatorial Paci c after the 1997–1998 El Niño event (Chavez et al. 1999) is particularly noticeable.”

“CO2 fluxes from central and eastern equatorial Pacific during the mature phase of 1997-98 El Niño reduced to 0.2±0.15 moles m -2 yr -1 and after the recovery from El Niño, these values surged to 2~6 moles m -2 yr -1 [Chavez et al., 1999].”

“The occurrence of ENSO conditions from October 1997 through April 1998 (Chavez et al., 1999) appears to have interrupted the winter/ summer pattern of high/low diatom production and sedimentation in Cariaco Basin.”

“…spring and summer in the tropical Atlantic and Pacific Oceans, the equatorial upwelling front exhibits north–south undulations on a scale of 1000 km (Legeckis 1977; Chavez et al. 1999) that shape the sea surface temperature and surface chlorophyll tracer fields in a series of troughs and crests.”

“By contrast, La Niña is characterised by upwelling-favourable trade winds that restore levels of primary productivity (Chavez et al. , 1999).”

“Dominant mechanisms governing the chlorophyll response to ENSO include changes in equatorial upwelling and thermocline depth (Chavez et al., 1999; Radenac et al., 2001; Wilson & Coles, 2005), and zonal advection (Picaut et al., 2001; Radenac et al., 2012; Stoens et al., 1999), all linked to…”

“…measurements at appropriately large spatial scales, since the profound effects of ocean climate on coastal and open-ocean ecological communities are often characterized by temporal lags and non-linear responses (Chavez et al., 1999; Hyrenbach and Veit, 2003; McGowan et al., 2003).”

“Nutrients and chlorophyll decreased sharply in the equatorial Pacific (Chavez et al. 1999) and relatively strongly in central California (Chavez et al. 2002), Oregon (Corwith & Wheeler 2002), and the Gulf of Alaska (Whitney & Welch 2002).”

“As expected, sea surface temperature anomalies (ΔSST) for the Niño3 region (Fig.”

“In November 1997, close to the peak of El Niño event, chlorophyll concentrations were less than 0.05 mg/m3 in the central and eastern equatorial Pacific and mean primary productivity was 35–40 mmol of C/m2/day-about half the climatological mean (Chavez et al., 1996; Chavez et al., 1999).”

“While linkage between climatic and oceanographic variability has been found in many marine organisms (Beamish et al. 1997, Mantua et al. 1997, Chavez et al. 1999, Hunt et al. 2002, 2008, Durant et al. 2006, Byrd et al. 2008), most studies did not address spatial components in climatic and…”

“Sea surface pCO2-SST relationships have been extensively examined in the equatorial Pacific [e.g., Boutin et al., 1999; Chavez et al., 1999; Cosca et al., 2003].”

“For example, Christian et al. (2002a) (Pacific regional model) and Gregg (2002) (global model) successfully simulate the large biological signals in the tropical Indo-Pacific associated with ENSO (Chavez et al., 1999).”

“…the fi rst Chl OC-CCI EOF mode illustrates the strong spatio-temporal signature of ENSO events observed in the Paci fi c Ocean (Figure 6C), with opposite Chl responses to ENSO-related physical anomalies observed in the eastern Paci fi c compared to the western Paci fi c (Chavez et al., 1999).”

“The variability in tropical Pacific Chl primarily arises from the modification of the east–west thermocline slope during the El Niño–Southern Oscillation (ENSO) (e.g., Chavez et al. 1999; Wang et al. 2009; Schollaert Uz et al. 2017).”

“…coral die-off at Galapagos when the El Niño Southern Oscillation (ENSO)-mediated reduction of major upwelling resulted in nutrient deficiency (Chavez et al., 1999) and an associated drop in surface water productivity in combination with exceptionally high water temperatures (Riegl et al.,…”

“Variability in iron fields is expected, both from variations in transport of the EUC on interannual (ENSO) and decadal timescales (Chavez et al., 1999; Le Qu er e et al., 2003; Le Borgne et al., 2002; Rodgers et al., 2008) and from variations in candidate sources, like the strength and depth of the…”

“El Niño events occur every 3 to 7 years and are characterized by warmer sea surface temperatures (SSTs), weak or absent equatorial upwelling, reduced primary productivity and a smaller ocean to atmosphere CO2 flux (Chavez et al., 1999; McPhaden, 1999).”

“…El Niño-Southern Oscillation) affect currents, temperature, and prey availability (i.e., distribution and abundance) thousands of kilometers away in the North and South Pacific and beyond (including terrestrial habitats over the Americas and Asia; Black et al. 2009; Chavez et al. 1999, 2003).”

“Indeed, the impacts of ENSO across the Pacific rely on large-scale oceanographicatmospheric perturbations that are rapidly and consistently transmitted along the Pacific coast of South America at interannual timescales (Chavez et al., 1999).”

“This climatic pattern emerges as the 2nd dominant mode of sea surface height variability in the Northeast Pacific and is well correlated with upwelling intensity and primary production along the California coast.”