plicity since it encompasses the conditions experienced in the Samoan EEZ), 4) a time series of available of series time a 4) EEZ), Samoan the in experienced conditions the encompasses it since plicity sim- for included is the EEZ (only the EEZ American throughout Samoa and American areas) water 3 2 1 km 80 of area an for extracted were characteristics ocean analyses, these (for respectively S) W,14.26 (170.2 Tutuilaand S) W,14.26 (172.66 Savai’i of islands the to close measurements ocean comparing variable each for patterns seasonal the of description finer-scale a 3) (EEZs), Zones Economic Exclusive Samoa and the of position the highlighting while and sensing remote the other data of that were analyzed, 2) description a broad-scale overview of brief the major ocean features a and processes at work 1) provides: assessment the variable, each For anomalies. height surface sea and chlorophyll, temperature, surface sea circulation, ocean waves, winds, include ment assess- this in variables Oceanographic Archipelago. Samoan the in ecosystems reef coral to importance of events anomalous and trends, variability, long-term inter-annual fluctuations, seasonal typical the scribe for thelastfewdecades. were usedtode- information datasets andothersupporting These satellite-based A diversity of satellite sensors has provided estimates of oceanic and atmospheric variables at global scales Da it where can exceed300mm/month.Inwinter(June-August),rainfallis30%loweratapproximately200 mm/month. (December-February) summer austral the in occurs rainfall Maximum ncdc.noaa.gov/CDO/cdo). (http://www7. topography on depending locally varies but year per inches) (120 mm >3,000 averages that temperature varies between 22°C and 30°C (SPSLCMP 2007). The air islands are daily noted for high Mean annual rainfall storms. cyclonic severe but infrequent and winds, trade northeasterly or easterly persistent The climateoftheSamoan humidity,high temperatures, air mild by year-round is characterized Archipelago Climate Background ences theymayhaveonSamoanreefecosystems. cur- waves, rents, sea winds, surface temperature, chlorophyll, including and sea surface height trends anomalies, and discusses potential and influ- conditions oceanographic and atmospheric regional of summary a provides chapter This 2010). al. et Barshis man etal.1999,USEPA 2007, Young 2007, change (ChaseandVeitayaki 1992, Timmer - reefs are presently in flux due to global climate and atmosphericprocessesaffecting Samoan oceanographic Many acidification. ocean and fluctuations, level sea temperatures, ocean ed elevat- as such phenomena climate-related of range wide a by modified and stressed be can other factors. Once established,reefecosystems and level, sea tides, nutrients, waves, winds, temperature, including the terize adapted to the climaticconditionsthat charac- those organisms that arrive and thrive must be on oceancurrentsand carried totheregion are archipelago the reach that Larvae Pacific. tions andprocessesofSouth the equatorial shaped inpartcondi by theoceanographic ecosystems intheSamoan are Archipelago and healthof The biogeographycoralreef Introduction American Samoa/DepartmentofMarine andWildlifeResources NOAA/NOS/NCCOS/CCMA Biogeography Branch NOAA/NOS/NCCOS/CCMA CoastalOceanographic Assessment Statusand Trends Branch t a nd Methods and Oceanography oftheSamoan Archipelago Doug Pirhalla 1 , Varis Ransi - 1 , MatthewS.Kendall Photo credit:MattKendall,NOAA,BiogeographyBranch. Image 3. A close-uplookatadiversebenthiccommunity. 2 at the same latitude excluding land and shallow and land excluding latitude same the at 2 andDougFenner 3

page 3 Chapter 2 - Oceanography page 4 Chapter 2 - Oceanography hury et al. 2007). The Southern Oscillation Index (SOI) measures the strength of the oscillation and is com- is and oscillation the of strength the measures (SOI) Index Oscillation Southern 2007). The al. et hury change in atmospheric pressure between the eastern and the western of the South Pacific (Chowd http://www.cpc.noaa.gov).(see CPCwebsite: et al.2004) Halpin croix 1999, is the Oscillation The Southern Samoan the within Del- and (Alory phenomenon climate (ENSO) Oscillation Southern and Niño El the with associated are of Archipelago aspects other many and winds of variability decadal-scale and Interannual in resulting northward slightly shifts stronger windsandlower rainfall(AloryandDelcroix1999). zone the August) – (June winter in whereas February) – (December months summer the during Samoan Archipelago the over established clearly most is It 1999). Delcroix and both a seasonal and interannual basis. The SPCZ crosses over the Samoan Archipelago twice a year (Alory cially during summer months (December-February). The SPCZ undergoes shifts in position and intensity on winds are generally westward/northwestward. This area of convergence results in heightened rainfall, espe- zone convergence the of south Tosouthwestward. the generally are winds zone convergence the of north 2.1). the (Figure To surface the at converge Winds Trade where (SPCZ) Zone Convergence Pacific South winter (July) than in summer (Merrill 1989). A major atmospheric feature affecting the Samoan climate is the in stronger typically are TradeWinds 2.1). Figure colors; (yellow-green southwest the to northeast the from blow winds surface where system atmospheric persistent a Winds, Trade the by dominated is region The cycle. Samoan the place Pacific, South EEZs into regional the context, and to in depict prevailing wind features patterns within the circulation archipelago over atmospheric a typical annual broad-scale the discern to used data are available at averaged a 25 km spatial resolution monthly for a 7-year period (July and 1999 to September 2007). Weekly Data were (http://www.remss.com/qscat/qscat_description.html). scatterometer wave QuikSCATthe micro- satellite’sby measured are surface ocean the near winds of direction and Magnitude Wind Results T are freelyavailableandshouldbedownloadedfromoriginalsources(T in specific years or months are highlighted in separate plots. Original remote sensing data used in this study occurred have that values extreme Such phenomena. short-term important obscure can but patterns sonal in all 21 years was averaged to create a composite seasonal cycle. This enables identification of typical sea- of data. For example, there were 21 years of sea surface temperature (SST) data. Average SST for January years all across averaged are means monthly plotted, are cycles annual Where patterns. seasonal convey to suitable were month other every for plots or averages monthly variables, most for that revealed analysis Preliminary analyses. in excluded were signatures water shallow or land with contaminated were that data satellite the in pixels Ocean ecosystems. reef coral to relevance particular of are that conditions anomalous and intensityof of thefrequency trends inclimatepatterns,and5)adescription multi-year data showing SST fronts GOES-10/11SST and Anomaly (CoRTAD)) Pathfinder SST andSST Surface Currents ERS-1/2ENVISAT Geostrophic Jason-1, Topex/Poseidon, QuikSCAT SeaSurfaceWinds Chlorophyll and Anomalies Chlorophyll SeaWiFS OceanColor Height Anomolies ERS-1/2ENVISAT SeaSurface Jason-1, Topex/Poseidon, able 2.1.Originaldatasources. PRODUCT TYPE AVISO, SSALTO/DUACS & AVISO, SSALTO/DUACS & Remote SensingSystems NOAA/NESDIS/NODC NESDIS/NODC/STAR DA T A SOURCE CNES CNES NASA 1985-2006 2000-2007 1992-2006 1999-2007 1997-2007 1992-2006 FRAME TIME RESOLUTION SPA 1/3º grids 1/4º grids 25 km 4 km 4 km 1 km TIAL able 2.1).

Weekly/Monthly Weekly/Monthly Weekly/Monthly Weekly/Monthly TEMPORAL Daily/Monthly Daily/Monthly SUMMAR Y

cm/s degreesfrom m/s, degreesfrom Steradian -1 UNITS µg L-1, north north cm ºC ºC - Samoan Archipelago. sea surface height anomaly (SSHA), and chlorophyll to demonstrate its relationship with ocean climate in the of SOI values is provided for reference alongside plots of several variables in the assessment including SST, Positive SOI values indicate La Niña episodes where equatorial Trade Winds are strengthened. A time series shifts the SPCZ to the north and coincides with higher winds in the Samoan region (Alory and Delcroix 1999). (VecchiPacific equatorial the in waters surface warmer and 2000) (Luick 2010).Winds Wittenberg and This Tradethe of strength in decrease a by characterized are which episodes Niño El indicate often SOI the of puted from the difference in atmospheric pressure at Tahiti and Darwin, . Sustained negative values atmospheric features and wind vectors (black arrows) are labeled in the plot for January at upper left. Odd numbered months are displayed. EEZsofSamoaand months American Samoaareoutlinedinthecenterofeachmap. numbered Odd left. upper at January for plot the in labeled are arrows) (black vectors wind and features atmospheric Key 2007. to 1999 from years the on based QuikSCATare the averages by Monthly measured satellite. direction Wind Figure 2.1. page 5 Chapter 2 - Oceanography page 6 Chapter 2 - Oceanography Brtw n Hu 19) wv ad ie eodr (riad n ohr 20) mdl sc a NOAA as such models 2008), others are and Waveexposures 1994). power Haug Wavewatch (Tolmanand III (Barstow altimetry satellite and (Brainard 2010), recorders tide and wave 1994), Haug and (Barstow Samoan the Waveriderof through climate extensively wave The characterized been has buoys Archipelago Waves where itcausedsubstantialdamagetobothterrestrialandmarineresources. Islands Manu’a the over directly almost going southeast to northwest from EEZs Samoan the of middle the CMP 2007) and variable damage to Samoan reefs (Tausa and Samuelu 2004). In 2005, Olaf passed through of the archipelago coming within 150 km of Savai’i (Fenner et al. 2008) creating a 0.3 m storm surge (SPSL- south passed Heta of eye the 2004, In 2.2). (Figure mph 155 over winds powerful sustained with storms very 5 Category and recent 2 including years 30 past the in Archipelago Samoan the near passed or struck have cyclones Six 2009). (Craig Pacific South the in storms cyclonic of development to conducive region a of edge eastern the along lie EEZs Samoan The above. described climate wind typical the from departures severe but infrequent are elsewhere) typhoons or hurricanes storms, tropical called (also storms Cyclonic Figure 2.2. Path andintensity ofcyclonespassingthrough theEEZsofSamoaor American Samoa from2000-2007. these currentsinSamoanwatersisvariableamongseasonsandyears. 2.3). (Figure (SECC) Current Counter Equatorial South (2) theeastwardflowing (SEC), and of Theintensity Current Equatorial South flowing westward the (1) 2004): Chen and (Qiu archipelago the affecting currents surface major 2 are there scale, regional a 2.3). At (Figure 2009) Craig 2004, al. et McClain 2003, Godfrey and 1999, Tomczak Delcroix and (Alory flow counter-clockwise a with currents a ocean Gyre, connected of Pacific series South the of edge northern the along lies Archipelago Samoan the scale, broadest the At Ocean circulation 1994, Brainardandothers2008). Haug and (Barstow islands the of coasts northern calm more relatively the on swells large unusually cause were recorded during Cyclone Ofa in 1990 and Heta in 2004) and even storms in the North Pacific which can heights wave m >8 (e.g. 2003) al et (Militello cyclones of passage the 2010), al et (Roeber tsunamis to due and Haug 1994). In contrast to the typical seasonal and interannual patterns, anomalous wave events occur regular as with other variables, there is some evidence that El Niño conditions ir- somewhat increase are wave SOI height the with (Barstow correlations 2008). Although al. et (Brainard directionality variable more and m), (~2 heights wave lower waves, period shorter by characterized often period a is March through vember No- 2008). al. et Brainard 1994, Haug and (Barstow latitudes higher at storms producing swell of frequency the Tradeof intensity and increased Winds the with common) is height wave m (2-3 May-September during highest are general in power wave and south the from swell Ocean 1994). Haug and (Barstow archipelago long period(~10-20seconds)“oceanswells”that originate from storms many of which arefar south of the versus Winds Trade easterly the as short such forces components, local from main result that two seas” into “wind seconds) split (~2-10 period be can climate wave 1994).The Haug and (Barstow years among and seasonally vary can but islands Samoan of coasts facing southern and eastern the on highest typically American Samoa areoutlinedinthecenterof themap. Figure 2.3.Major surface currents of the Southern adapted from Tomczak and Godfrey (2003). EEZs of Samoa and page 7 Chapter 2 - Oceanography page 8 Chapter 2 - Oceanography of sunlight is higher than its mean annual value (Alory and Delcroix 1999). Regional maps of monthly mean monthly of maps Regional 1999). Delcroix and (Alory value annual mean its than higher is sunlight of intensity the as long as increases SST that intensity,indicates sunlight which maximum the behind months three SSToccurs Maximum March. in C 29.5° of in high C a 27.2° to of low August a from C 2° proximately high and stable ocean temperatures throughout a typical annual cycle (Figure 2.4). Average SST ranges ap- At the edge of the equatorial Pacific warm water pool, the entire Samoan Archipelago experiences relatively vide animportantrecordoflocalizedtemperaturevariability. pro- and (2008) others and Brainard by detail in discussed are data These Division. Ecosystem Reef Coral been recorded by data loggers deployed at several near shore locations around American recently Samoa have data by temperature NOAA’swater Continuous archipelago. the of waters the in events SST low or high or unusually cycle, and identifyanomalous nual an- average an over EEZs Samoan the within Archipelago into context, depict changes in SST the South Pacific, place the SST of the Samoan were usedtodiscernthebroadSST patternsin Monthly averaged data for the entire time period 2008). (Selig km 4 of resolution a at 2005) ber Decem- to 1985 (January period year 20 a for estimates SST average weekly produced has al Reef Temperature Anomaly Database,which Cor- the for basis the are data variables. These other and cover vegetation cover, cloud global and reprocessesseasurfacetemperature, measures which (AVHRR) Program, Pathfinder Radiometer Oceans Resolution High Very Advanced NOAA/NASA the by globally lected Sea surfacetemperature(SST) data arecol- Ocean temperature be discussedingreaterdetailChapter3. currents and implications for larval transport will (Tremltions in patterns Finer-scale 2008). al. et na- island adjacent and Archipelago Samoan the in islands among connectivity and transport larval on influences major are patterns Current Savai’i (green). of EEZ the for to values adjacent average waters Tutuiladenote (red), Colors Samoa 2006. American to and 1985 (blue), from data Figure 2.4.

SST (C) 27.5 28.5 29.5 27 28 29 30 Jan Sea surface temperature data from CoRTAD presented as an average annual cycle. Monthly averages are based on based are averages Monthly cycle. annual average an as CoRTAD presented from data temperature surface Sea Feb Mar Apr American Samoa EEZ May Image 4.Bleachedacropora.Photo:D.Fenner, ASDMWR. Jun Jul Aug Sep Savaii Oct Nov Dec warmer thanaverageconditions. major El Niño of 1997-1998 showed generally positive SST anomalies in the Samoan Archipelago, indicating of ~1° C from 1985 through 2006 (p < 0.0003, R 0.0003, < (p 2006 through 1985 from C ~1° of increase an exhibit EEZ Samoa American the within SST in trends Overall 2.6). (Figure patterns irregular more and seasonal both revealed data anomaly temperature and SST available of series time year 21 The productivity (Polovinaetal.2001)areessentiallyabsentfromtheSamoanEEZs(Figure2.5). biological face temperaturefrontsthatfrequentlyoccurathigherlatitudesandareassociatedwithenhanced SST.sur- in Sea variation longitudinal minimal is There Islands. Samoan the of rest the around those than the American Samoa EEZ in any in given season latitudinally such range that SSTwaters around C ~1° are 0.5 a – is 1° C there warmer average On 2.5). (Figure patterns seasonal gradual reveal SST American Samoa areoutlinedinthecenterof eachmap. and Samoa of CoRTAD.EEZs from 2006. temperatures to surface 1985 Figure 2.5.Sea years the on based are averages Monthly 2 = 0.05, SST = 28.1 + 0.0023*month). All years since the since years 0.0023*month). All + 28.1 = SST 0.05, = page 9 Chapter 2 - Oceanography page 10 Chapter 2 - Oceanography a metric called Degree Heating Weeks (DHW) is often used to highlight peak periods. It is a weekly metric weekly a is It periods. peak highlight to used often is (DHW) Weeks Heating Degree called metric a bleaching, and stress coral in role a plays elevated are temperatures water the time of length the Because spread events documented in the summers of 2002 (Fisk and Birkeland 2002) and 2003 (Fenner et al. 2008). in American Samoa (Craig 2009) with a severe event in 1994 (Goreau and Hayes 1994) and additional wide andappearwhite. algae (zooxanthellae) Three recent events havebeendocumented major coralbleaching symbiotic their expel will corals time, of period short a even for high especially are temperatures or enough 1990). persists forlong temperature and ifthiselevated threshold” the “bleaching is called This temperature 1° C above the highest temperature expected in the summer, corals can become stressed (Glynn and D’Croz typic, or reef building corals, require warm tropical water, however when Herma- ocean Archipelago. temperatures Samoan are the higher than in reefs on corals the for high too become also can temperatures Water and uncertaintyoftheeffects ofclimateoscillations(SPSLCMP 2007). may be related to the rapid shift from El Niño to La Niña conditions during 1998, and highlights the complexity 19 years of available data. This strong negative Samoan SST is a potential lag effect from the 1997 El Niño, Samoan the in values negative strong with coupled other the in seen not pattern a 2.7), (Figure Archipelago is that 1998 July in SSTregion negative equatorial strong the the in is anomaly note Of correlations. perfect Inspection of other SOI patterns reveals that the SST/atmospheric interactions are complex and do not yield EEZs. Samoan the in values expected from change little but equator the SSTalong cooler show anomalies July the 2001) 2000, 1999, 1989, (e.g. conditions Niña La during (1998), exception notable one With 2.7). Samoan EEZs during this time was 26.5°C, approximately 1°C the cooler within SSTthan conditions. average Niño during El both strong years of (Figure indicative -2, than less of values SOI persistent featured 1997 SOI values negative but begin peak several months during prior occur (Alory and generally Delcroix 1999)(Figure Temperatureminima 2.6). 2008). For example, al. July 1987 et and Fenner 1999, Delcroix and (Alory Samoan Archipelago the in occur conditions SST cooler generally and 2007) al. et (Chowdhury Pacific ern During strong El Niño years significant warming of ocean temperatures occurs in the equatorial central/east- region. the in pronounced most are Niño El of effects the when anomalies, temperature (July) winter on ing given year are affected in part by the Southern Oscillation (Alory and Delcroix 1999). This is shown by focus- The seasonal SST range of 1-3° C is evident in all years. The specific range and temperature extremes in any positive values. strong with orange by represented are conditions Niña La values. SOI negative strong with blue dark in represented are conditions Niño El NOAA/NWS. from are period time same the for values (SOI) Index Oscillation Southern Samoa. of American EEZ the for averages Valuesmonthly 2006. are to 1985 CoRTADyears from the values for anomaly and temperature surface Figure 2.6.Sea

SST (C) SO Index (SOI) 26 27 28 29 30 -8 -4 0 4 58 78 99 19 39 59 79 90 10 30 506 05 04 03 02 01 00 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 58 78 99 19 39 59 79 90 10 30 506 05 04 03 02 01 00 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 Southern Oscillation Sea Surface Temperature - waters near Savai’i and Tutuila (Figure 2.8). Elevated DHW (>4 degree C) for occurred at irregular 1985-2006 intervals with for calculated was (CoRTAD),DHW TemperatureDatabase Reef Anomaly Coral the Using higher, or DHW 8 is widespread bleachingand mortalityfromthethermalstressislikely. stress thermal When likely. is bleaching coral significant DHW, 4 of value a reaches on Based threshold. bleaching the research conducted at NOAA’sabove Coral Reef Watch is (http://coralreefwatch.noaa.gov/), when the thermal stress temperature the degrees of number the as well as threshold bleaching the exceeded temperature the when weeks 12 previous the of number the on based calculated and American Samoaareoutlinedinthecenterofeachmap. Figure 2.7. Sea surface temperature anomalies from CoRTAD during the month of July for the years 1997 to 2005. EEZs of Samoa page 11 Chapter 2 - Oceanography page 12 Chapter 2 - Oceanography NOAA Coral Reef Watch indicated an average SST of 30° C for an area that included an in situ temperature satellites (Brainard and others 2008). In an extreme example, on one day in 2005 satellite measurements by on based those than higher C 1° to 0.5 temperatures sustained recorded Island Swains Tutuilaaround and reefs on deployed loggers temperature situ in the of most fact, In here. used approach based satellite the low circulation, may produce bleaching conditions in particular lagoons and reef flats that is not predicted by light, and incident conditions, depths, wind shallow including other factors,primarily water temperaturesand stress conditions in ~1/3 of the last 15 years. An important caveat to interpretation however, is that localized thermal to Samoan subjected the been of have reefs Archipelago coral the that suggest data these Overall, in watertemperaturethatcanoccurtheregions (e.g.Figure2.9). variability localized the to due likely are here and Tutuilaexamined Savai’i sites the and site monitoring tual likely. is bleaching coral significant vir- Ofu which the for between threshold Differences DHW DHW in 4 the surpassed Ofu at temperatures where mid April through March late from weeks several of period a tracked from January to March of 2003. During this period, NOAA Coral Reef months consecutive Watch three during issued times 3 at bleaching occurred warnings This threshold. and bleaching the above rise site Ofu the at years ofdatadidSSTthe nine watches wereissued.Onlyoneyearduring low andnobleaching consistently through May experiencing a watch at some time during nearly all nine years of data. Only in 2008 were SSTs January of months Summer/Fall core the with June and November between months all NOAAin by issued were watches bleaching 2009 to 2000 From W). 170° S, SST14° on at centered pixel km 50 a in measured based station- monitoring virtual (Ofu of Samoa Islands American Manu’a the in Ofu off waters on based is and here considered those than site different a at conditions bleaching monitors Watch Reef Coral NOAA dent intheregionatthesetimes. evi- is DHW increased of band patchy but extent. Alatitudinal spatial their in variability considerable reveal series time the in events DHW peak during snapshots Regional region. this in DHW and SOI between ship relation minimal be to appears there series, time anomaly SST the Unlike 2008). al. et Fenner 2009, Craig 2002, Birkeland and Fisk 1994, Hayes and (Goreau events bleaching coral documented to corresponding stress exceeded 4 DHW in Savai’i and/or Tutuila in 1991, 1994, 2001, 2002, and 2003 with 3 of these years (April-May). Thermal Fall in occurred generally values DHW Elevated 1990. since observed peaks stronger Figure 2.8. SO Index (SOI) (°C) -8 -4 0 4 0 1 2 3 4 5 58 78 99 19 39 59 79 90 10 30 506 05 04 03 02 01 00 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 58 78 99 19 39 59 79 90 10 30 506 05 04 03 02 01 00 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 Degree Heating Weeks Southern Oscillation Sea surfacetemperatureanomalyplotsforwarmestwatermonth. Tutuila Savaii - resolution. Chlorophyll a is the dominant pigment in marine photosynthetic organisms and measuring its con- measuring and organisms photosynthetic in marine pigment a isthedominant Chlorophyll resolution. ten-year (September 1997to October 2007) datasetof estimated chlorophyllconcentration, at 9-km spatial a provided satellite (SeaWiFS) Sensor Field-of-View Wide Sea-viewing the from dataset color ocean The Chlorophyll (Craig etal.2001). with bleaching associated typically thermal conditions to withstand able and localities with somecorals 2002) bleaching events, the severity can vary widely across islands in the Samoan Archipelago (Fisk and Birkeland widespread for Even 2008). on Tutuilaal. airport et the (Fenner near pools lagoon two in documented been always well predicted or detected by satellite based monitoring. Annual coral bleaching from 2004-2008 has satellite- on based those derived surface estimates (Brainard and others 2008). than This indicates that localized bleaching events are not lower C 1° typically values recorded Ta’uaround loggers temperature situ in contrast, In 2008). al. et (Fenner Samoa) (Fagaitua, American C 34.9° of value a recorded which logger Figure 2.9. Bleaching alerttime-seriesfromNOAA CoralReefWatch. page 13 Chapter 2 - Oceanography page 14 Chapter 2 - Oceanography approximately 8°SandtothesouthwestnearIslandsofFiji. rate of 1.4% per year (Polovina et al. 2008). Slight chlorophyll increasesare evident just north of the EEZ at a at expanding be to shown recently region a 2004), al. et McClain 2004, al. 2.11)et (Figure (Dandonneau the at lies archipelago July.The in µg/Lnorthwestern edge of 0.08 a distinct region near of minimal oceanic high productivity associated to a with the South to Pacific Gyre 0.02 January in range µg/L 0.05 averages of Chlorophyll low a 2004). from µg/L al. 0.03 et McClain 2004, al. et (Dandonneau 2.10) (Figure ability vari- seasonal discernable but limited very with year all levels chlorophyll low shows archipelago entire The waters ofthearchipelago. the Samoan EEZs over an average annual cycle, and identify unusually high or low chlorophyll events in the patterns in the South Pacific, place the Samoan Archipelago into context, depict changes in chlorophyll within using SeaWiFS color sensors. Monthly averaged data for this period were used to discern broad chlorophyll cal productivity. Chlorophyll a concentration, referred to simply as chlorophyll in this report, can be estimated centration in ocean waters provides one measure of nutrient input to surface waters and subsequent biologi (blue), andSavai’i (green). Tutuilato adjacent waters (red), Samoa of American EEZ the for values average denote Colors 2007. to 1998 years the on based are averages Monthly cycle. annual average an as presented and SeaWiFS from estimated concentration Figure 2.10. Chlorophyll Photo: D.Fenner, ASDMWR. Image 5.RedalgalbloominPagoHarbor.

Chlorophyll (ug/L) 0.045 0.055 0.065 0.075 0.05 0.06 0.07 0.08 Jan Feb Mar Apr American Samoa EEZ May Jun Jul Tutuila Aug Sep Savaii Oct Nov Dec - 2007. Oddnumbered monthsaredisplayed. EEZsofSamoaand American Samoaareoutlined inthecenterofeachmap. Figure 2.11. for the entire EEZ of American Samoa during the same months. The limited spatial extent of these events is averaged was concentration chlorophyll when evident was change Minimal 2.13). (Figure archipelago the of islands smaller other the around ocean the in not but Tutuila,and respectively Savai’i near waters ocean in evident were µg/L 0.2 to µg/L 0.12 of increases chlorophyll subtle 2005, and 2002 of (April-June) winter fall- During 2.12). (Figure chlorophyll in increases episodic short-lived two shows series time 10-year The Chlorophyll concentration estimated from the SeaWiFS satellite. Monthly averages are based on the years 1998 to 1998 years the on based are averages Monthly satellite. SeaWiFS the from estimated concentration Chlorophyll page 15 Chapter 2 - Oceanography page 16 Chapter 2 - Oceanography that characterize theregion. results inclear water, deep lightpenetration, andconditions suitablefor growth of the coral reef ecosystems round. This year productivity biological low concentration, have and poor nutrient are EEZs Samoan of chlorophyll waters oceanic the in spikes small, very but episodic, and seasonality measureable some Despite Rose andSwainsatolls (0.2-0.25 µg/L). of 0.7 µg/L) with lower values for Ofu, Olosega, and Ta’u (averages of 0.3-0.4 µg/L) and lower still values for most populated island Tutuila, showed the highest and most variable concentrations of chlorophyll (average than those measured by satellite farther offshore reported here. Nearshore water samples for the largest and 2008). These nearshore samples typically showed an order of magnitude higher concentration of chlorophyll March 2006 were analyzed for chlorophyll and nutrient concentrations by NOAA CRED (Brainard and others February/ during Samoa of American and islands the around km 1-2 within collected samples Water have greaterlandareaandhigherhumanpopulations (Brainardandothers2008). nutrient inputs at these times elevated the chlorophyll levels around the larger islands in the archipelago that deflected by the larger islands. Another possibility is that rainfall runoff and associated terrestrial and human Samoan the across be directly can flows and which years SECC, some the during for Archipelago flow high the archipelago could cause the elevated chlorophyll signature (Brainard and others 2008). April is a time of chlorophyll heightened and (Domokos et al. enrichment 2007). It is also possible that topographically induced upwelling around the larger islands of nutrient localized of areas in result could mixing resulting The 3). the SECC during the fall-winter (March-June) time frame could promote eddies and meanders (see Chapter of circulation eastward and EEZ the of side north the on SEC the of circulation westward Enhanced 2001). al. et Strutton 1997, al. et Foley 1996, al. et (Barber EEZ the inside activity eddy increased of result the are anomalies chlorophyll these that speculated is It phenomenon. climatic large-scale with associated not ally gener are events episodic These 2.13). (Figure 2005 April and 2002 June for plots regional in highlighted conditions arerepresentedbyorangewithstrongpositivevalues. Niña La values. SOI negative strong with blue dark in represented are conditions Niño El NOAA/NWS. from are period time same of EEZ to adjacent waters (black), Samoa American Tutuilathe for values (SOI) Index Oscillation Southern (red). Savai’i and (blue), the for averages Valuesmonthly 2005. are to 1997 years the for SeaWiFS from estimated concentrations Figure 2.12.Chlorophyll Monthly Chlorophyll (ug/L)

0.04 0.08 0.12 0.16 0.24 SO Index (SOI) 0.2 -6 -3 0 0 3 6 Chlorophyll Southern Oscillation Oct-97 89 00 20 40 60 08 07 06 05 04 03 02 01 00 99 98 Jan-98 Apr-98 Jul-98 Oct-98 Jan-99 Apr-99 Jul-99 Oct-99 Jan-00 Apr-00 Jul-00 Sep-00 Jan-01 Apr-01 Jul-01 Oct-01 Jan-02 Apr-02 Jul-02 Oct-02 Jan-03 Apr-03 Jul-03 Oct-03 Jan-04 Apr-04 Jul-04 Sep-04 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06 American Samoa EEZ Samoa American Savaii Tutulia Apr-06 Jul-06 Oct-06 Jan-07 Apr-07 Jul-07 Oct-07 Jan-08 Apr-08 - Niña conditions arerepresentedbyorangewith strongpositivevalues. La values. SOI negative strong with blue dark in represented are conditions Niño El NOAA/NWS. from are period time same the for values (SOI) Index Joint Oscillation Center Southern Data Level. Oceanographic Sea Center/National for Level Archive Sea U. from Valuesare 2008. Data to Pago, averages. 1948 Pago monthly from for are Samoa values American level Figure 2.14. Sea ed mean sea level is created from T/P data for the estimat- of map a Tolevel. SSHAs, sea calculate mean expected from deviations vertical to refers (SSHA) Anomaly Height Surface Sea satellites. Poseidon (T/P), Jason-1/2, ERS-1/2 and Topex/ENVISATthe from data height surface sea merges of Interpretation (AVISO)Data in Oceanography Satellite Program and Validation Archiving, The on theseinstruments. tsunamisignalsarealsorecorded the associated and events Seismic tidesandcurrents.noaa.gov/). range of 2.51 ft as measured at (http:// go consist of two highsand lows dailywithamean this site (SPSLCMP 2007). Tides in the archipela at estimate reliable a more to establish is needed time seriesofdata a longer although 1993-2007 period the for mm/year) (4.9 rise level sea of rate if nothigher shows asimilar Data fromthisgauge in level sea Samoa. measures , which gauge Fine Resolution Equipment) Acoustic Measuring Level (Sea SEAFRAME a operates which CMP), Sea Level and Climate Monitoring Project (SPSL- is Pacific level South the by region the in monitored Sea also 2.14). (Figure noaa.gov/sltrends) Pago Pago at (http://tidesandcurrents. present the to 1948 evident from is CI) (95% 0.90 ± mm/ 2.07 year of level sea mean in trend positive A trends. level sea and tides of context the in stood Anomalies inseasurfaceheightarebest under Sea surfaceheightanomalies

Mean Sea Level (mm)

1000 1100 1200 1300 1400 SO Index (SOI) 900 -8 -4 0 4 8 9115 9116 9117 9118 9119 012006 2001 1996 1991 1986 1981 1976 1971 1966 1961 1956 1951 9115 9116 9117 9118 9119 012006 2001 1996 1991 1986 1981 1976 1971 1966 1961 1956 1951 Sea Level Southern Oscillation - - are outlinedinthecenterofeachmap. Samoa American and Samoa of EEZs 2005. April and 2002 June for SeaWiFS from estimated anomalies Figure 2.13. Chlorophyll page 17 Chapter 2 - Oceanography page 18 Chapter 2 - Oceanography shift of this anomaly across the archipelago in the band of elevated heights can be seen from March to May. southward 2.16). Ageneral Figure red; (circled March in noted are 5°S) (~ Islands Swains around EEZ the of side northern the on anomalies height surface sea Elevated region. the in level sea in variations spatial predictable somewhat reveal month by SSHAaveraged global of Maps the 1993-1999. for calculated to level sea relative mean expressed and positive are 2.16 Figure in SSHAs all that Note 2.15). (Figure cm ~4 lies are highest in winter (May-August) and lowest in summer (December-January) and have a range of only The entire Samoan Archipelago experiences similar changes in SSHA during a typical annual cycle. Anoma- unusual orextremeobservationsofSSHAsanddiscusstheirrelevancetocoralreefecosystems. identify and EEZs, Samoan the in SSHAs of patterns inter-annual and seasonal depict context, into EEZs and used to discern broad patterns of sea level fluctuation in the South Pacific, place SSHAs of the Samoan ways for the study region. A 15 year dataset (1992-2006) of monthly mean SSHAs was obtained from AVISO several in evaluated and plotted were level sea mean this from deviations Observed tools/hdbk_duacs.pdf). in reference to mean sea level during this period (http://www.aviso.oceanobs.com/fileadmin/documents/data/ period January 1993 to December 1999 at a global scale. All deviations in sea surface height are presented Image 6.Exposedcoralsonareefflat,southern Tutuila. Photo:D.Fenner, ASDMWR. Savai’i (green). Notethatthescaleisrelative totheglobalmeansealevel fortheperiod1993to1999. the years 1993 to 2006. Colors denote average values for the EEZ of American Samoa (red), waters adjacent to Tutuila (blue), and Figure 2.15. Sea surface height anomalies from AVISO are presented as an average annual cycle. Monthly averages are based on SSHA (cm) 0 1 2 3 4 5 Jan Feb Mar Apr American Samoa EEZ May Jun Jul Tutuila Aug Sep Savaii Oct Nov Dec the strong El Niño of 1998 (SPSLCMP 2007). Sea surface heights in the EEZ averaged 25 cm below normal Oscillation (Alory and Delcroix 1999). A major negative height anomaly Southern occurred in the the Samoan to EEZs during response significant a have Archipelago Samoan the in SSHAs emerge. patterns key eral sev- series, time year 15 a as shown are instead and years across averaged not are values monthly When defined from winterthroughspring (alsoseeCurrentsSection). and intense less become and dissipate currents and SSHAs These 2007). al. seasonal et corresponding (Domokos shifts their and SECC and SEC the of signature the represent heights elevated These months aredisplayed.EEZsofSamoaand American Samoaareoutlinedinthecenterofeachmap. Figure 2.16. Sea surface height anomalies from AVISO. Monthly averages are based on the years 1993 to 2006. Odd numbered Odd 2006. to 1993 years the on based are averages AVISO.from Monthly anomalies height surface Sea page 19 Chapter 2 - Oceanography page 20 Chapter 2 - Oceanography ~30 cm lower than the expected monthly average. In fact however, when coupled with the right environmen be to level sea for was observed deviation maximum The ecosystems. reef coral to significance little have they that magnitude low such of be to seem first at may here reported level sea mean from deviations The of 0.58 between SOI and height anomalies at eight months following SOI minima (Alory and Delcroix 1999). value a found that analysis correlation lag a corroborates This region. the for interconnections atmospheric ocean- strong the emphasizing 2.19), (Figure 0.081*SOI) + deviation|=0.034 level |sea R2=0.63, 0.001, < (p strength Niño El and anomalies level sea negative of magnitude between relationship positive significant a indicate regression the of results The (http://tidesandcurrents.noaa.gov). Services and Products graphic NOAA’sfrom obtained was 1770000) (station Oceano- Pago Operational Pago for at Center observed level www.cpc.noaa.gov/). For each El Niño event, the corresponding maximum deviation from monthly mean sea NOAA’s(http:// the Center from Prediction obtained Climate was observed value (standardized) SOI lowest the 1954, since event Niño El documented every For conducted. was SOI versus SSHA of regression ear lin- a (SOI) Niño El the of strength the with correlated was drop level sea of magnitude the Toif determine 1999). Delcroix and (Alory SOI the behind months eight roughly occurring values anomaly height greatest 4-8 years with the frequency of the anomalies being directly related to the timing of negative SOI values with hury et al. 2007). Based on this time series, low water conditions can be expected in the Samoan EEZs every 1992 (Figure 2.14). All of these low sea level anomalies correspondto documented El Niño events (Chowd and 1987, 1983, 1978, 1973, 1966, 1958, 1954, in drops level sea revealed also but 2005 and 1998 in etry Pago, SSHAPago altim- the for satellite confirmed data in Samoa level depicted American sea events term of because 2.1), (Figure SPCZ the of the in the strengthandposition changes Trade WindsandtheSEC(Figure2.3)(SPSLCMP 2007).Long- with closely corresponds Niño El by affected most is level sea where area The ~3,000km. of distance a Islands, Solomon the to Islands Cook central the from Pacific South the affected March, in extent largest its at SSHA, lower of band east-west 2.18). An Figure blue; (circled years other in month same the to comparison in 2005 and SPSLCMP2007) see (and SSHA1998 March for plots in evident is EEZs, Samoan the beyond well anomalies, height negative these of extent spatial broad very The Archipelago. Samoan the in level sea mean below cm 10 dropped heights surface sea vertical where cific (SPSLCMP 2007). Another noteworthy event correlated with an El Niño occurred during March of 2005, during March-April, 1998 (Figure 2.17). This event was recorded by sea level gauges widely in the South Pa- are conditions represented in dark blue with Niño strong negative SOI values. La Niña El conditions are represented by orange with strong NOAA/NWS. positive values. from are period time same the for values (SOI) Index Oscillation Southern Samoa. American Figure 2.17. period averages Figure values. Sea surface height anomalies from AVISO for the years 1993 to 2006. Values are monthly averages for the EEZ of EEZ the for averages monthly are Values 2006. to 1993 years the for AVISOfrom anomalies height surface Sea

18.

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- - survival during average SSH conditions. Coral colonies and branches within the same colony are observed are colony same the within branches and colonies Coral conditions. SSH average during survival Coral tides. colonies low in the reef flat zone of have flattened tops that clearly height demarcate water depths suitable for the growth and to tied closely is flats reef on corals of limit growth vertical The Archipelago. Samoan the in islands the of most around ecosystems coral the of component extensive an up make flats Reef flats. reef of communities coral on impact major a have can events level sea low these conditions, tal American Samoaareoutlinedinthecenterofeachmap. Figure 2.18. Sea surface height anomalies from AVISO during the month of March for the years 1993 to 2006. EEZs of Samoa and page 21 Chapter 2 - Oceanography page 22 Chapter 2 - Oceanography Counter Current. Equatorial Current, andtheSouthEquatorial South Zone, Convergence Pacific South the shifts infeaturessuch as by thelatitudinal primarily influenced is This year. the on ing depend tures thantherestof archipelago differentslightly fea- or atmospheric oceanic chain, isaffectedas theSamoanisland by spot hot volcanic same the from derived not and EEZ Samoa American the of extremity mates. Swains Island, located in the northern Samoa liein essentially identical oceancli- here demonstratethatSamoaand American examined variables most expected, As tude. bylongi than latitude by significantly more much vary Samoan Archipelago the for mate Delcroix 1999). Nearly all aspects of ocean cli- processes (Aloryand ed morebyinterannual whereas and seasurface chlorophyll heightareaffect SST- and waves, winds, for sonal ENSO. sea- is variability of source major The in climatic cyclessuchas to larger response fluctuations multiyear larger much and often conditions ocean in fluctuations sonal sea - by small can Samoaarecharacterized of Samoaand The islandsandatolls Ameri- Conclusions should beafocusoffutureresearchtoinformcoastalplanningforreefflathabitats. events such of severity and periodicity, extent, the predicting and Understanding 2.18). (Figure Pacific the of areas vast affect can events height surface sea low that indicate here presented images could Satellite mortality result. coral and exposure flat reef phase, in are conditions these of intensity and number critical some or all, When flats. reef exposed cooling and moistening, covering, regularly from swash wave prevent seas Calm height. surface sea low of periods during exposed corals desiccates and heats angle sun high and cover cloud low by measured as radiation solar High waves. and winds, light, incident to related likely tent of the event next depends on additional factors most ex- and Severity magnitude). cm (~-4 patterns seasonal with documented El Niño cases (~-30 cm magnitude) and associated events inter-annual include report this by ed anomaly. seasurfaceheightdocument- Factorsreducing must be presentatthesametimeasalowseasurfaceheight tide low a occur, to event exposure an For coral. as “kaimasa”,aterm related to the odorfrom decaying unpublished data). Locally, refer to such events Green, (Alison 1998 in Samoa American in researchers by documented was tides” low “extreme corresponding of corals diedduetoandthe sea surfaceheightanomalies A massive reef flat mortality event during which up to 84% als andfatalconditionsforlargeareasofthereefflat. cor- of exposure in resulted indeed has limit growth their as established have corals flat reef the that tide lowest 1-2 cm. An anomalous drop in sea level 30 cm below the within of growth vertical uniform remarkably a achieve to - - Photo credit:M. Anderson. Image 7.Flattoppedcoralhead. 94 p 001 R=.3 |e lvl eito|004 + deviation|=0.034 0.081*|SOI| level since |sea R2=0.63, events 0.001, Niño < p El 1954. during SOI versus deviation level sea monthly maximum of regression Figure 2.19.Linear Max. Monthly SL Deviation (m) *-1 0.1 0.2 0.3 0 1980 1970 1954 2005 1964 1 1958 1973 1978 1966 SOI* 1992 1987 - 1 2 1998 1983 3 tions (USEPA 2007,Barshisetal.2010). to suchperturba adapted an reefsthaninregions Samo - on affects greater have may change climate by exacerbated trends or anomalies oceanic tions, condi stable relatively with region a in developed have archipelago the of reefs the that Given 2010). their near thermal tolerance(Craiget al. 2001, Barshiset al. living already corals to threat serious a pose temperatures water Advisory Increasing 2007). Reef Group Coral 1992, Veitayaki and (Chase zone coastal lying often low and into anarrow ed crowd- already to ahumanpopulation implications chi and Wittenberg 2010). Sea level rise has obvious (Vecpatterns intheregion precipitation long-term - the eastward expansion of the warm water levels, pool, and sea Samoan affect to continue will charac- teristics and activity ENSO 2008). al. et (Polovina year per 1.4% of rate a at expanding be to shown been recently have Gyre Pacific South the with ated chlorophyll and biological productivity values associ- 2007, Young2007, Barshisetal.2010). The low VeitayakiUS EPA1992, 2007,VecchiSoden and (Chase and climate change to global in response monitoring the oceanic characteristicsof the region continue to important is It 2009). al. et Brown 2008, ence and500-1,000yearsold(Brainardothers circumfer- in m 41 to up are colonies Porites Some archipelago. the of extremity eastern the Ta’uat of nies intheworldsuchasthoselocatedoff theisland of some of the largest individual hermatypic coral colo- growth and survival long-term very the allowed have that factors the among be may conditions of resiliency.reef of context the constancy relative The in considering Sa- worth is environment reef coral moan the of stability relative This latitudes. lower or higher at observed SST than variability interannual range of values, fewer extreme fluctuations, and less S latitude. The SST in thisregionhasamuchsmaller 17° and 10 2.20). between roughly (Figure lie EEZs Samoan latitude The S 30° and S, 25° S, 20° S, 15° S, 10° S, 5° 0°, and and moa Samoa) American Sa- between boundary approximate (the longitude time series plots of SST at the intersection of 170° W to thenorth. upwelling through This isdemonstrated ature frontsthatoccurfarthersouthandequatorial fluctuations such as subtropical sea surface temper- unaffectedgenerally bythemoredynamicocean to areasthenorthandsouth. The is Archipelago compared conditions oceanic region stable a relatively with in lies Archipelago Samoan the Overall, - - ⁰C ⁰ ⁰C ⁰C ⁰C ⁰C ⁰C C 20° S,25°and30°Slatituderespectively. tween Samoa and American Samoa) and 0°, 5° S, 10° S, 15° S, intersection of 170° W longitude (the approximate boundary be- Figure 2.20.SeaSurface Temperaturefrom CoRTAD atthe 28 30 32 24 26 28 30 32 24 26 28 30 32 24 26 28 30 32 24 26 28 30 32 24 26 24 26 28 30 32 24 26 28 30 32 25 0 15 10 30 1985 20 5⁰ ⁰ ⁰ S (equator) ⁰ S ⁰ S ⁰ S ⁰ S S 901995 1990 2000 2005 page 23 Chapter 2 - Oceanography page 24 Chapter 2 - Oceanography EPA). (Oceanographer,Samoa Wiles American Phil and Vetter(NOAA/NMFS/PIFSC/CRED), Oliver Commerce), ture Conservancy), Clare Shelton (Coral Fellow, Coral Reef Advisory Group, American Samoa Department of Brainard (NOAA/NMFS/PIFSC/CRED), Jamison Gove (NOAA/NMFS/PIFSC/CRED), Alison Green (The Na- Russell Foundation), Climate (The Kelley Anderson material: this of drafts to comments review and mation The authors wish to thank the following individuals for contributing valuable discussions, data, general infor- ACKNOWLEDGEMENTS International CoralReefInitiative. GlobalCoralReef Alliance. Chappaqua,New York. 201pp. Goreau, T.J. and R. Hayes. 1994. Survey of coral reef bleaching in the South Central Pacific during 1994: Report to the coral mortality. CoralReefs8:181-191. Glynn, P.W. and L. D’Croz. 1990. Experimental evidence for high temperature stress as the cause of El Niño coincident Research II44:1801-1826. 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